Continuous Glucose Monitoring with Medtronic/MiniMed Updated

WARNING: SEVERELY OUTDATED! I’m seeing this get some traffic again. I just want to be clear. This post is from 2007! Medtronic sensors are a whole lot better than this now.

I decided to create a new post for this so that my initial reaction to continuous metering would remain untouched and available for review. If you would like to see my first reactions to this device, please refer to my original post on the same topic.

I am now at the point where I am satisfied with the sensor glucose readings about 75% of the time. This has taken me a number of months, despite the fact that I consider myself quite technical and quite good at caring for my diabetes. Thus far, the sensor has helped my go from an A1C of 5.8 to 5.3, an improvement of about 9%. I do not know yet whether my next A1C will be as good. My doctor has cautioned be about going low too often. Being even more careful about lows than I had been may raise this slightly.

So, the number one topic you need to know about in order to get results is also the hardest to understand and the hardest to get straight information about.

ISIGs: ISIG is short for Interstititial SIGnal. This has nothing at all whatsoever to do with the strength of the transmission signal between the transmitter and the insulin pump. (Or presumably, the CGM device if you are not using one of the new pumps that serves both functions.) The sensor inserted beneath your skin has enzymes on it that react with your interstitial fluids to produce a “signal”. Personally, I would call this the raw glucose reading. However, a representative from Medtronic just assured me that this is not the case. She even assured me that it is possible for the ISIGs to be rising or falling while the reading is doing the opposite. I’m remaining skeptical about this point at this time. I have not seen that happen and do not understand how the simple measuring of the rate of reaction of the enzyme can produce two numbers.

She also assured me that valid values for the ISIGs while attached to a sensor in your body are 2 – 200. In my experience, 12 – 25 or so is far more normal. When my ISIGs drop too low, especially below 10, it’s a really good bet that the pump is telling me that my glucose is low, sometimes very low, and is another good bet that the value is completely unrelated to my actual blood sugar, which can even be high at such times.

I have requested any internal documentation they have on the meaning of ISIGs. If I get a more detailed answer, I will update this post.

RULE #1: No matter what else is happening, no matter how insistent the device is being about wanting a blood glucose calibration, DO NOT GIVE IT ONE WHILE THE ISIGS ARE LOW!!! Doing so is the number one way to get wildly inaccurate results. I’ve seen 200-300% discrepancy in sensor and blood glucose readings after calibrating during low ISIG times. It is far better to acknowledge the message, move around, massage the sensor area, or just plain wait an hour or two until it comes back to normal before calibrating. At worst, that will leave you with an hour or two of no sensor readings.

Rule #2: Wear your electronics (cell, crackberry, whatever) on the opposite side of your body from your pump. The transmitter is using the frequency that provides for maximum interference with all other electronic devices. Wear your pump as close to your sensor/transmitter as possible. If you put a cell next to your pump, you will frequently get weak signals, often followed by lost sensors. This is a royal pain in the butt. If you work in a modern office with WiFi, cell phones, blackberries, cordless headsets, microwave ovens, and all the rest, keep an eye out for weak signals. By the time it warns you, you will have only about 5 minutes to run outside for a while until the connection is reestablished. This happens to me somewhat regularly. I am seriously hoping for a wire connection option at some time in the future. I’m already tethered to the pump. Having two tethers would be better than all of these weak signals.

Rule #3: If you hope for the pump to warn you about highs and lows, set the range of values much tighter than you expect to keep it. There is a 15 minute lag (at least) between a change in your blood sugar and a change in the interstitial glucose value returned by your sensor. Setting tighter limits will warn you earlier. If you respond to these alerts appropriately (I always recommend checking blood glucose before taking action on the alert), what will happen is that your sensor will show lower amplitude swings in your glucose than your actual blood sugar values. This is because you are circumventing the peaks and valleys before they get to the interstitial fluid. So as an example, your graph may show a range of 68 – 140 when your readings show 50 – 180.

Here is the routine that has been mostly working for me to get reasonably accurate data from the sensor most of the time, beginning with sensor insertion day.

  1. Remove prior sensor the night before and charge the transmitter. This doesn’t take long, so can be done that morning if you wake even earlier. If you do this the night before, you’ll want to disable the sensor feature on your pump for the night. Your settings and existing graph will not be lost.
  2. Wake up at least 2 hours and 15 minutes or so before breakfast, 2 and a half hours may be safer.
  3. Remove the sensor from the refrigerator.
  4. Clean the area for the sensor with soap and water and dry thoroughly. This makes your skin less oily so the tape will stick better.
  5. Insert the sensor according to the instructions.
  6. Place a strip of tape over the flat portion of the sensor. It does not have enough tape of its own. Where it does have enough is on the wrong side. 3M makes a gentle paper tape that holds well and doesn’t irritate my skin when left on for 6 days. The tape Medtronic gives doesn’t hold well and doesn’t breath.
  7. Wait 5 minutes to ensure that the site does not bleed.
  8. Reenable your pump’s sensor feature, if disabled from the prior night. Tell pump to begin a new sensor.
  9. Connect transmitter to sensor and watch for green blinking light on transmitter.
  10. Check that the pump is receiving the signal from the transmitter.
  11. Wait a few minutes and check that the pump is receiving ISIGs from the sensor (Press ESC four times to get to that screen). The ISIG values may vary tremendously during this time. As long as they are non-zero, it should be fine.
  12. Attempt to keep your blood sugar flat during this time. You may wish to check your blood sugar now. I usually do.
  13. Wait for the pump to request a reading, check blood sugar and tell the pump the value. This wait period is when I usually go to the gym, making this a good schedule for me.
  14. Now you can take insulin and eat breakfast, even though you will not be getting sensor readings for another 15 minutes.
  15. Check your blood sugar an hour or two after breakfast and attempt to stabilize it. The 6 hour reading that it will want, just before lunch is a good time, is probably the biggest source of my poor calibrations since I am sometimes not as stable as early morning.
  16. You do not need to wait the full 6 hours for the next reading. Whenever you are stable, usually before lunch, is a good time to enter a reading.
  17. Throughout the rest of the sensor life, whenever I do a reading, if I am stable and the ISIGs are good, I enter the reading. This way, I am usually not forced to provide a reading when I am unstable or my ISIGs are bad.
  18. On the third morning, before the pump registers that the sensor is too old and kills it, tell the pump you are using a new sensor. Immediately after this, tell the pump to Find Lost Sensor. The pump will ask you for a new calibration now and another in 6 hours. But, you will not need to wait 2 hours before giving the pump the first calibration. It’s a useful little hack to work around the need to lie to the pump to get 3 more days from your sensor. Note: Sometimes I find that the 6th day doesn’t give accurate readings. Lately it has been. Some of my sensors may not have been adequately refrigerated for their entire life, making them last a shorter time. I’m not sure.
  19. Note: If you feel that your sensor is really badly calibrated, following step 18 above may be a good way to recalibrate from scratch without any CAL ERRORs. I’m not positive about this at the moment. Let me know if it works for you. I’ll update this if I verify that it works for me every time. I’ve had far fewer cases of poor calibration lately, so have not needed this much.

Settings that have been working well for me:

  • High warning 130, snooze 2 hours.
  • Low warning 70, snooze 1 hour.
  • Alarm reminder 45 min.
  • Cal reminder 2 hours, gives enough time to stabilize.
  • Missed data: 40 min.
  • I also tend to change to vibrate for the day and long beep for the night. (Main menu: Utilities->Alarm->Alert Type)

Let me know if this helps you at all. Please also feel free to share your own experiences in the replies. If you prefer to stay anonymous about your medical condition, feel free to use an alias and bogus email.

FYI: It appears that this post has been replicated at this diabetes site. If you like this post, perhaps you’ll go there and rate it. Of course, if you don’t like this post, A) Why did you read this far and B) Please don’t rate this post on that other site ( just kidding, mostly 😉 )

UPDATE 1/11/2008: (Data below is empirically derived, not from Medtronic/MiniMed)

SENSOR ERROR: I’ve gotten this error a few times now. I usually get it during the startup period of a brand new sensor. It’s tempting when seeing this to believe that there is a real problem with the sensor. There isn’t!! Or, at least there may not be. Hit ESC four times to get to the screen with next calibration time and ISIGs. If the next calibration time has simply moved an hour or so forward, your sensor is still good. The ISIGs merely haven’t stabilized yet. Do nothing. Wait for it to ask for a reading. The sensor will likely still be fine for days. I think I wasted a sensor the first time I saw this, $30 down the drain.

CAL ERROR: I tend to get these whenever I’m having trouble with ISIGS. The problem is that the pump will immediately ask for a new reading. DO NOT DO A READING IMMEDIATELY!! You’re very likely to get another CAL ERROR or two and lose your sensor if you do. Try moving around and massaging the sensor site. Or, just wait an hour or two until you see normal ISIGs again, over 10 is usually OK if your reading is below a hundred or so, over 15 is better. When you have good ISIGs, then give the pump a calibration reading again. This will leave you with no readings during the time you are waiting. But, you lived without continuous glucose monitoring before. It’s not life sustaining, just very helpful. You’ll do better calibrating when your ISIGs are good and just clearing all requests to METER BG until then.

166 Responses to Continuous Glucose Monitoring with Medtronic/MiniMed Updated

  1. Staci says:

    Thank you for your sensor insight. I have had the mm/sensors CGMS for 3 weeks now and have had a bad batch of sensors. MM send new within 24 hours and that made me happy but what a pain with the insertation.
    I am now thinking about the upper arm as an insertion site. My belly area gets knocked around alot with waist bands, belts etc.
    I liked your ISIG info. I spoke with MM over Xmas and they told me that the values could be off as much as 20%. I said I understand the timing and all but if my BG is 68 and the pump says 148….thats a problem….thus bad sensor again even after a restart.
    I have had Type one for 47 years and being able to watch or monitor my levels is a god send if working and I know there will be improvements to this system also.
    I still take insulin using a pen; no problem with that now. Thanks again for your insight.

  2. Jane says:

    I started using Minimed sensors this past December, and am frustrated over the results, so your posting has some helpful information. Good stuff they don’t teach you in the training. I sent my isig readings and other data to minimed, but they haven’t gotten back to me. So I’m not even sure if I have bad sensors or not.

    About half the time, the meter and sensor readings are 20+ points apart. I had a similar experience with a sensor of 142, and meter was 68. Fortunately, I ‘felt’ low, and knew the sensor was wrong. Another time, sensor said 140, and meter was 240.

    I will try some of your suggestions regarding the calibration, and see if that helps.

    I’ve had type 1 diabetes for 43 years, and on pump for 10 years.

  3. Misanthropic Scott says:

    Hi Jane,

    Stick with it. It’s never going to be perfect. You’ll always need to watch your ISIGs, especially when the sensor tells you that you’re low, it may just be that your ISIGs have gone bad. But, it is definitely worth it, even with the months long learning curve.

    Let me know if any of the tips I’ve posted here have helped. Please post any additional tips that you find on your own. In my experience, a lot of this is still being learned empirically.

    When I learned to pump insulin, 10 years ago for me too, MiniMed had diabetics as trainers. They were pump users themselves and knew the pump well. This has not been my experience with the continuous glucose monitoring. I do not know whether Medtronic has a different philosophy or whether they are having trouble getting enough diabetic employees. Either way, I agree that the training is no longer up to par.

    So, for those of us that care enough to want the best available care, I think we’re a bit more on our own than we used to be. Let’s try to join together to share all the information we can.

  4. Jane says:

    Hi Scott,
    Today my calibrations did much better (or I was much smarter). When I awoke, my first meter reading was 66, and sensor was 82, isig was < 10. No Low alarm because it’s set to 80. I had some juice to bump up the 66, and decided not to use that as a calibration, since the juice would cause a quick rise. An hour later, meter was 148, sensor 142, isig was 11.8, so I did a calibration then. The rest of the day, the sensor and meter were pretty close, and isigs between 11-18 Prior to your note, I would have done a calibration at 66, and I think that would have caused havoc. I checked my downloaded data table from earlier days, and see several days where I had isigs less than 10, followed by CAL ERROR and BAD SENSOR errors.

    My trainer mentioned the isigs, but it made it sound like it was ‘too technical’ to tell me what to look out for. Said the numbers were for Minimed to use, not the user.

    A tip I found on another blog suggested changing the sensor at night time, but leaving the transmitter on the charger overnight (new sensor inserted, but not attached). Then in morning, attach the transmitter, and they said the first calibration is in minutes instead of 2 hours. That might work better for me, than getting up 2 houirs early as you suggested, and I’ll give it a try on my next change.

  5. Misanthropic Scott says:

    Great Jane!! I’m glad to hear I could be of some help. I hope it continues to work for you. Interesting point about the sensor overnight. My morning gym routine leaves me with enough time. I may try that though, especially when on travel or when I don’t expect to get to the gym for whatever reason.

    I got the same impression about ISIGs initially too. However, after several times of having problems and being asked about the ISIGs, I knew I needed more information about them. Diabetes care works best when we’re intimately involved in our own care. The more educated we become the better we do, IMHO.

    Doctors and other health care providers are (or can be) great. My doctor is fantastic. However, I’m still the one dealing with my own diabetes 24×7 around the world or at home. Every bit of knowledge helps. I don’t ever expect to be perfect. I just want to always do the best I can.

  6. Marnie Franze says:

    okay found out about ISIG from the medtronic help line…. Take a blood test, and divide it by your ISIG number. If the number is between 1.5 and 20 then you can calibrate. Calibration will not work if the number is outside of that range. Knowing life there might be exceptions….

  7. Marnie Franze says:


    Once the sensor stops after 2 bad calibrations. Can you restart it telling the pump that it is a new sensor?or is it done for ever and ever…..

    Love your site, thank you,


  8. Misanthropic Scott says:

    Hi Marnie,

    Once it’s dead from 2 bad calibrations, I have not successfully gotten it back. This is one of the reasons that I like to check ISIGs before doing a calibration. Also, when I get a CAL ERROR, I never attempt to calibrate immediately. I just clear the error, live without the sensor working for an hour or two or sometimes three until the ISIGs look good again. Then, I calibrate.

    That’s great information about the ISIGs. Thank you very much for sharing it.

    It also confirms my suspicion that the ISIG number is essentially the raw glucose reading. It just requires that for each sensor, and for the same sensor as the reactive chemicals on the sensor are reduced, that the number be translated to an actual mg/dL reading.

    I imagine that an ISIG of 15 sometimes means 100, sometimes 80, sometimes 120. This likely depends on the flow of interstitial fluid to the site, the individual sensor, individual body chemistry, and possibly additional factors as well. However, I do not think there is any additional information in the ISIG other than a speed of the reaction with the glucose in the interstitial fluid, despite my last conversation with Medtronic.

  9. Jane says:

    I got one to start again after a 2 CAL ERRORs by doing a start new. My training material says to unplug the transmitter first, but I don’t recall doing that. It also says to use the ‘test plug’. if it occurs again. But it worked when I just did a start new. I may have first turned the sensor setting off, then on, then start new..

    My CAL ERROR occured when sensor said 40, and meter said 101, and I tried to do a calibration. isig was 4.21. Obviously I now know not to calibrate in this situation, but those false LOW alarms were annoying. Meter bg / isig = 24, so that matches with what Marn said.

    I had noticed in my ‘data table’ of downloaded data, that there is a ‘calibration factor’. Sure enough, it is the Meter BG divided by the isig. (or very close).. Then if I look at the readings after the calibration factor, looks like it is multiplying the isig by the most recent calibration factor.. My calibration factors range from 8 – 18. kinda makes sense, except why does it take the pump 15-20 minutes to update the calibration factor !!!

    So the isig * conversion factor is what determines the sensor reading, and if either is out of whack, so is the reading.

  10. Misanthropic Scott says:


    My guess about why it takes so long for the pump to update is that it is trying to account for the 15-20 minute lag between blood sugar changes and interstitial fluid changes. For sugar to get from blood to interstitial fluid just takes that long.

    I haven’t bothered to get an official word on that. It just always made sense to me since my doctor warned me before I got it that it was delayed.

    For anyone unaware, you should also not treat low blood sugar or take insulin based solely on the sensor reading. That said, when I have a sensor that has been performing well and am at a dinner party or other food fest where I expect my blood sugar to be climbing, I do sometimes take small amounts of insulin based on sensor readings. I tend to find it more rare for the sensor to be artificially high than artificially low, especially since I won’t calibrate with low ISIGs. So, it’s mostly off when the ISIGs drop erroneously and give a falsely low reading.

    BTW, Jane, another thing I do when the false low alarms bug me enough is I edit my settings and temporarily disable the low alarm. Just remember to turn it back on later,

  11. gail says:

    My son has been on a pump for 7 years, is very lean, and inserts in his belly region. For the CGM, he tried first to have it in his belly, but it was too painful. Next time (after a 2 month break), he put it into his upper thigh, where it was successfully in for 10 days. However, this time he reinserted, he got leg pains, which he reports having to a lesser extent the first time.

    Does anyone have ideas on insertion sites for a lean teen?

  12. Misanthropic Scott says:


    I’m thin by U.S. standards, a tad chunky by world standards (5’7″ & 165 lbs), probably not nearly as lean as your son, by my guess.

    I’ve been doing well with my buttocks. I usually go toward the upper or side to avoid actually sitting on the site. I do find some disadvantages in this. When I sit for a long time, especially in a car where I really can’t move around as much as in an office chair, for example, sometimes my ISIGs drop ridiculously low or merely remain stable when my sugar is actually increasing.

    I also find though that the times this happens are in only such extreme cases of immobility, not around the house or office. For comparison, I also find that at such times as long drives and flights, that my insulin absorption is slow to non-existent.

    So, while I will say that I have some trouble with this area once in a while, it is still good enough that I use it nearly exclusively.

    I should also add that I also almost exclusively use my thighs for insulin infusion and have not noticed any problems with this, even when my thigh infusion site ends up 3-4 inches from buttocks sensor site, though I think this is not recommended.

    So, I’d say to advise him to try the upper and outer butt for a while and see how it goes.

  13. Mary says:


    Just want to say thank you for sharing all this information. I just started with the MM CGMS 3 days ago and you’re experience has really given me a head start. Especially the ISig stuff.


  14. I’ve been using the MM CGM for about four months now, and so far my results have been iffy. This is all great information that you’ve compiled, Scott, and much of it I had discovered already t hrough trial, error, and lost sensors. One thing I’m wondering about — has anyone tried the Dexcom? I test drove it and in the end I decided not to go with it, because I liked everything showing on my pump. But now I think I wish I’d gone with Dexcom. I found their sensor to be much more accurate, albeit bulky and LOUD! The alarms are relentless. However, the range of the Dexcom was significantly better too. Ah well, it’s all first-generation technology, and I’m lucky to have the option of using it at all. For this I am grateful. Thanks again for all your helpful information.

    Save Our Plants: Eat Them!

    • Tom Coats says:

      Greetings from Texas!

      I read this entire exchange of comments and useful information with a great deal of interest until arriving at the Dexcom comments.

      I had the previous two models of Dexcom devices until recently requesting the Medtronic 530.

      My class with Medtronic instructor started with a comment like “Dexcom is a bad word for us, and we are not going to talk about them”!

      So far I would say that the Decom devices I used were far more accurate, reliable and dependable than the Medtronic sensors.

      With wide swings between highs and lows, I was generally within a few points of the Dexcom reading and actual glucose measurements.

      Never did I have the large differences between sensor and actual glucose readings I have with the Medtronic device.

      I am a senior citizen, and as generally assumed, reluctant to try new things, but that reluctance has NOT influenced my evaluation between the Dexcom and Medtronic sensors.

      The best thing about the Medtronic sensors, in my humble opinion is that they are much less likely to be snagged, or uncomfortable when worn due to their lower silhouette.

      They are less accurate, more difficult to insert and secure, have a shorter life, and are more complicated.

      I am hoping for rapid improvement and more reliability with whatever improvements Medtronic makes with newer models of pumps and sensors.

      San Antonio, Texas

      • Jeff says:

        Haven’t done Dexcom. I had the older Medtronic / SoftSensor GCM and it basically sucked. Wild readings, constant sync issues, weak signal, calibration errors, and only to be rewarded with the constant “warm-up” periods,

        The 530 pump + Enlite sensors are a comparable dream. Sensors last 6 days (honestly, but you can push another day out of them easily if you have a well-charged transmitter). Much more accurate, no calibration errors so far, and they will calibrate sooner.

        That, plus the 530’s threshold suspend are a dream. No EMT visits since I upgraded and last A1C was 6.3 (my lowest since diagnosis).

        As you noted though, 530 is still a brick on your belt 🙂 Considered a leather case or sport case to try to make it a little less obvious, but appears you can’t easily hide the beast.

      • That’s great information Jeff. Thanks a lot. I’ll be looking into whether I can make the switch to Enlite sooner, rather than waiting until my pump is out of warranty. I’m not sure insurance would cover that. Perhaps they will with a letter of medical necessity from my doctor.

        I don’t care about the brick or being asked why I still have a pager. I’m always willing to explain anything to the curious. I find it makes others much more comfortable with my diabetes when I’m willing to discuss it. Else people have weird preconceptions and misconceptions about what it means to live with diabetes. Mostly, it causes them to express surprise when I eat chocolate. But, it can be worse than that.

  15. Misanthropic Scott says:


    I was not aware that an alternative exists to the Minimed continuous glucose monitoring, or at least not a similar technology. Glucowatch has been around for quite some time. My doctor recommended against it for a number of reasons based on limitations of that technology.

    The Dexcom appears to use the same or very similar technology to the Minimed version. I would therefore expect very similar limitations.

    Did you find that they dealt with the issues of the lag between blood glucose and interstitial glucose better than minimed? Were there fewer problems related to times when interstitial fluids are just not moving around much?

    Have you experienced greater or lesser communications between the transmitter and the receiver? (Working in a modern office, I often get weak signal warnings, even when the devices are within 3 or 4 inches of each other. The frequency chosen for this communication by Minimed happens to be among the most susceptible to interference.)

  16. Bowdenski says:

    I have been using the Continuous Glucose Sensor for Months with mixed results. Often they work very well, but it is a shame that the are not programmed to weigh calibrations only during periods of stable ISIG readings. I have had problems with sensors and whole boxes of sensors. Currently have trouble when it gets a ISIG of zero, then starts to re-init.

    I really wish that the carelink software allowed the users access to all of our OWN data. It would be great to compare the ISIG, Glucose and the calibrations and the ratings of how close the monitor has been to meter readings. After we upload, thyey have this, but we can’t see it. Can anyone suggest better software ?

  17. Jane says:

    I agree.. I also have mixed results, and just this week got a 0.00 isig when first inserted (at 2 hr bg check). I waited it out and it finally got ‘normal’ after 15 hours. I get a few in a row that work great, and then the next few are so inconsistent, it’s not worth it. I’m considering trying my thighs to see if it makes a difference.

    I don’t like Carelink either, I’ve written to their support on several improvements, and get told ‘we’ll send it on to our marketing dept’… You can get access to the isig data in the Sensor table report, and I think it can be downloaded to CSV. I also hope for better software, and preferably one with local PC data storage, not the internet. (The MM Solutions software is even more limited than Carelink, and I heard no longer being enhanced by Minimed )

  18. Staci says:

    Hey is my 3 month CGM update…back in December it was definitely all about insertion of the sensor; now not a problem and cal errs, sensor errs etc. In retrospect I probably caused it. I love the idea of the true diabetics training for the CGMS.
    I now have leraned how to extend my sensor life up to 8 days. And truly even at the end the readings are still good. But after 8 days if Sensor Ends I do replace it.
    My true belief is that (and I was not told this by the trainer) a good calibration is the key to go CGM readings. NEVER calibrate during a rapid low or rapid high. If your calibrations are bad it will wear down the life of your sensor; I know that is true and that is something else I have learned.
    But the knowledge is priceless. My BCBS is not yet paying for the sensors but I am working on it. Knowledge is everything. And learning the trends of my bs has helped me a great deal to adjust as needed. This is by no means a perfect system but I am thrilled to have it. I am using the 522Paridigm as my CGM but not as a pump yet. Medtronic has been very helpful and it is appreciated.
    Tyoe 1 47 years

  19. Misanthropic Scott says:


    That’s great!! Thanks for sharing the info.

    I would highly recommend using the paradigm as a pump as well. I’ve been pumping for 10 years now. I can’t imagine how I had pretty decent control without it. Here are some of the advantages I’ve found from pumping:

    1. Using only Humalog, the insulin is not sitting there waiting for me to become active and go low. The insulin gets in and gets out. This is great if you’re active, especially unexpectedly. I used to get frequent lows from old insulin lying in wait for me to become active and then being absorbed at exactly the wrong time.

    2. Varying basal rates. I no longer see the dawn effect. My basal is 0.25 units/hour from midnight to 3:30AM. Then it changes to 0.75 (up from 0.65 on the advice of my sensors) to avoid the dawn effect. Then, at 8:00AM, it goes down to 0.1 for the rest of the day. These rates allow me to stay flat when not eating at any time of day, giving tremendous flexibility.

    3. Bolusing in public places couldn’t be easier. It’s either as easy as looking at your paradigm for sensor info CGM or easier if you buy the remote control.

    4. Bolusing very small amounts for very minor corrections is just as easy. I often find myself taking boluses of 0.3-1.0 for glucose in the 130-150 range.

    5. And, of course, one needle insertion covers 3 days of injections.

    6. Patterns. I can create basal rate patterns for days of differing activities. I have one for skiing where my midday basal starts earlier and is half my normal rate. Actually, this is largely because skiing is cold. I find I need a lot less insulin when out in the cold for long periods. I also have a pattern for safari, that I haven’t used in a while, with a higher basal rate during the day for sitting in a vehicle.

    7. Square waves are a great way to take insulin for large meals or slowly digesting foods.

    8. Temporary basal rates are great for hiking (turn down the basal) or long drives (turn up the basal) for a fixed amount of time. I just wish the pump didn’t feel the need to remind me once per hour that I’m on a temporary rate. I set it. I want it that way. Leave me alone already.

    The only downside I find with pumping is being tethered to the device. After a month and a half, my reflexes learned not to pull out the tubing on various cabinet knobs and other things. Your reflexes will need to sense the tug and jerk you to a stop before pulling out the infusion site. So, you may go through a bunch of extra sensors during this learning period.

    I sleep with the pump just loose in the bed and do not often get tangled in it or pull it out in any way. It took me longer to get used to not pulling out the sensor than the infusion site due to the dangling transmitter. The extra tape I use helps with that. The infusion sites don’t need any extra tape. The silhouettes I use have enough.

    Stay healthy!
    (Type 1, 20 years)

  20. Dennis Steed says:

    Not trying to be pedantic, but ISIG is actually signal current in nanoamperes as opposed to VSIG which is signal voltage (I is the standard abbreviation for current and V is the standard abbreviation for voltage). The I in ISIG has nothing to do with interstitial.

    The internal software for the 722/522 pump (as well as the Guardian and CGMS devices) has an algorithm for converting the current output of the sensor to a glucose reading. ISIG is a way of looking at the raw current data before the algorithm processes of it.


  21. Misanthropic Scott says:

    Thanks Dennis!!

    Your explanation sounds much better than the one I got from Minimed/Medtronic, which I posted above. It also matches much more closely with my experience, as I mentioned in the main post. I stated there that it seemed much more like “the raw reading”. Your explanation clears it up perfectly.

    As an aside, I had asked Minimed for any internal white paper they had on the subject. I never got the white paper or the call back on it.

    BTW, pedantic is a positive quality with respect to anything technical. I’m a programmer by trade and have often said that anal-retentive is a positive quality in a programmer. It helps with understanding this technology as well.

    Much appreciated,

  22. Jane says:

    Hi Scott,
    is your basal really .1 most of the day and .75 in early am ? Sounds like you must be very active ! My night and day are much closer (,5 – .8). I also have a rise at 4am. I use the temp basal too, and I agree.. why does it have to keep reminding me ? But it’s not as bad as the sensor alarms..

    With my sensors, I have learned that just getting up in the morning sometimes raises my bg, regardless of getting up at 7 or 10 !. But sometimes, it stays level in the am (w/o eating anything). Still trying to figure out a pattern on it.


  23. Misanthropic Scott says:

    Hi Jan,

    Those really are my basal rates, yes. After my honeymoon period ended, so probably 18 or 19 years or so ago, I had a daily intake of insulin of about 70 units a day, total. When I moved to Manhattan, I joined a gym and went religiously 4-5 times a week for a while. My daily intake dropped to about 25 units a day.

    Today, I go less religiously than that but still take about 22 – 35 or so, depending on whether I’m on a full day eating frenzy with friends or doing my usual routine.

    It’s all about insulin sensitivity. Exercise lowers your insulin requirement while exercising. Exercising regularly reduces insulin intake longer term. I wouldn’t worry about relative numbers between different people though. I only worry about my own insulin intake. Even then, I mostly worry about it with respect to maintaining tight control.

    I do not find getting out of bed to be significant regarding my morning insulin need. Whether I get up at 5AM or 10AM, I need the morning rate from 3:30AM to 8:00AM. The only time I vary it is for skiing. I want the insulin out of my system before I even start.

    I have found that being out in the cold for prolonged periods halves my basal requirement. Even when my activity is low, such as a camping trip we took to the arctic some number of years ago, I still have to reduce my insulin. I even dress very warmly for such activities.

    What I would do for determining basal is go by the mornings when you haven’t eaten. Eating will confuse the issue because you have too many variables, food, basal insulin, and bolus. This is just my recommendation, not my doctors. I would also only change basal rates overnight based on a few similar observations from evenings that are typical.

    When I changed my 4-8AM rate from 0.65 to 0.75 and adjusted the time to 3:30AM, it was based on regular evenings, not the ones where I had a huge dinner and drank, etc.

    Similarly, if you have a day where you have a late or no lunch, that is probably a better indicator of daytime basal needs. Even better would be a day when you have a Sunday brunch at noon or 1:00PM. If you can get your basal to keep you flat during that time, it is likely correct, IMHO.

    And, of course, only make changes based on the sensor’s readings for days when it is well behaved. That’s sort of a duh, but needs to be said anyway.

    Good luck!

  24. this is a response to Marie, regarding the two bad Cal Error messages. You can’t get that sensor back, but you can trick it into going again. The same way you can get more than 3 days out of one sensor. You have to go to your settings and turn the sensor Off for a few minutes, then turn it back on and select Start>New Sensor. So basically it thinks you’re giving it a brand new one. I get between 6-8 days out of one sensor.

  25. Jack says:


    Did medtronic ever give you any internal docs on the transmitter? If so did you sign an nda? I was wondering if there is a protocol for the data from the transmitter. It would be nice to get another device to receive the data and display where you want. I do know that they transmit on 916.5mhz which is the ISM(Industrial Science and Medical frequency) Fairly unfortunate because so many other devices transmit in the 900 mhz range like your phone, tv etc. If you have any info hook me up.

    Thanks, Jack

  26. Misanthropic Scott says:

    Sorry Jack. I am not privy to any inside information. I’m just trying to help people get started with technology that is about at the state of cell phones of the early nineties, i.e. not yet ready for prime time but still too useful to ignore.

  27. Chris says:

    I found a great item at Walgreens to tape my sensors and transmitter to my body. It is Walgreen’s brand “Skin Closure Strips” For Small Cuts. You get 30 strips in the box and they are 1/4 in wide (perfect for sensors) by 4 inches long. I keep my sensor in for up to 12 days (that has been my max so far since starting in Feb.) and these strips keep my sensors and transmitter in place! I acutally cut one strip in half to use over the sensor and a full strip for the transmitter. A little bit of alcohol gets the sticky stuff off of the transmitter when I disconnect or change the sensor. Hope this helps. I had been trying so many items to keep the products attached to my body and I so thrilled to have found this item! Hope this info helps others.

  28. STACY KW says:

    Hi Scott –

    I have been a pump user (MM) for over 5 years and just started on the CGM about 4 weeks ago. I just called MM last night to discuss returning the pump/transmitter b/c I was so unhappy with it. I was not getting warnings for my highs and lows, felt that my trend graphs held bad data and I did not see the point of using it. I felt like I was meter testing more than I did before just to see how far off the mark the sensors were. I’m good about testing before meals but often forget to test post meal or to write the info down in a timely manner (before the info clears out of my pump/meter). I thought the sensor would help me in this regard. After talking to MM a few times over the last few weeks with no help, I actually got a really good person on the phone last night and although I’m still not convinced I’m going to keep it, she encouraged me to try to make it work (again). I’m hoping the sales rep will approve an extension of my trial period otherwise I have until 3/25 to return it.

    I’ve taken some notes on the pointers you and the other folks have provided and will see if they help. This ISIG business was hardly touched upon other than to say make sure the value is between 2-200. I’m going to keep a close eye on that based on your info.

    A few questions…

    The MM tech person I spoke to mentioned that it’s not a good idea to calibrate immediately before a meal if you are going to bolus and eat immediately b/c the calibration activity takes about 20 mins and if you eat and bolus this could confuse the calibration process b/c your sugar would be fluctuating during this period. Have you heard anything about this? What are your thoughts?

    MM no longer sells the the cable that connects the meter to your computer so that you can download your sensor info. I was told by MM that the cables were not that well made and there is a new meter coming out so they are probably not stocking them anymore. Any idea where I might buy one? I’ve tried looking on ebay and a general google search, but have had no luck.

    Sorry for the long message. I’m just so frustrated and don’t know if keeping the new pump for the sensor feature is worth it. I’ve always been happy with the MM pump, but this sensor is not what I expected.



  29. Misanthropic Scott says:

    Hi Stacy,

    I hope you stick with it. I think you’ll get good information from it eventually that will make it worthwhile, despite the fact that it will likely continue to be frustrating.

    I have no trouble calibrating immediately before a meal. However, based on readings from the sensor, I have started taking my insulin earlier, unless my reading is low, which tends to mean that I do have a bit more time between the calibration and the meal.

    Still though, I would say it’s more important to get the calibration done when your blood sugar is in a normal range and not moving rapidly and definitely make sure the ISIGs are good.

    I do not use the cable and do not upload my data to MM.

    Good luck.

  30. Staci says:

    Stacy…I too was very frustrated in the beginning and still I can get upset when my sensor is not a match to the meter.
    But it is not a perfect device. What I feel for me is that is is an INDICATION of my blood sugar trends. That is what helps me bolus as needed after a bg reading.
    For me I think it is slow to pick up the low’s but excellent on the high readings. 10-15 minutes behind the meter for me typically. I still say calibration is the key start point.
    I am thrilled to be able to use it and for me much smaller than the dexcom. (I am sensitive to size because of bathing suits and waistbands).
    I was frustrated at first and probably had Medtronics send me new sensors because I thought I had bad ones. What I was doing was bad calibrations and bad insertations. All ok now but subject to change. Again, I dreamed of having an indication of trends and to catch them early.
    I think it will only get better.

    Type 1 47 years

  31. Ivy says:

    Scott & everyone…, Thanks so much for all the helpful information!! I was desperately in search of a “support group” for CGMS users &w as in tears after 1st getting my CGM (have used MM pump for 16 yrs).The sensor info was always really all off ,once-like 200 when I was really over 300.I was getting all the different kinds of alarms all night the first night all night. A lot was probably due to calibrating at the wrong times (my trainer never said don’t calibrate before a bolus) & maybe the device had problems too.After one week-the buttons on the pump wouldn’t work.Grrrrr. I called the Support line & did some tests they directed,but ithe pump still would not work.I was told it quit due to static electricity & they sent me a new (“refurbished”) pump.They also told me I needed to use the pump in a pump case (poly or leather-not just the clip) to help about the static problem.On another call to them,I was told some dryer sheets around the pump helped. My goodness…with all the technology that went into this…
    Sensor readings are better- still I’m disappointed in the whole thing. Thanks to your site , will keep trying.Does anyone know how long you can use sensors past the expiration date.Mine expire in August 2008 (purchased a 3 month supply through “coinsurance)?With learning I can use one sensor more than the 3 days,I may have paid for excess. (and we know they are expensve. Stacy,do you need the cable with the white box on the end to attach your BD meter? -I have an extra one you can have (but for whatever reason I have to put a new battery into the meter every time to get it to download. So I only download before quarterly Dr.visits). Also a MM local rep said it wouldn’t hurt anything to travel in an airplane with the sensor on.I did that & had no problems.
    Best wishes to all of you & thanks again for or your helpful comments.

    Type 1 18 years

  32. Misanthropic Scott says:

    Ivy, In your example of a sensor reading of 200 when you are really 300, I would not be at all surprised. One thing to keep in mind is that the sensor is at least 20 minutes behind your blood glucose. Assuming that you see a sensor reading of 200 and check your blood sugar and see 300, it seems highly likely to me that you would treat that high blood glucose. I know I would.

    Therefore, you will start to bring your blood sugar down before your sensor fully has time to register it. So, your sensor might go up to something like 220 or 240 and start coming down because you’ve taken insulin. I generally expect a lower amplitude in my sensor readings because I treat either high or low blood sugar with fast acting humalog or glucose depending on which way my reading is off. This causes the glucose reading to turn around before the sensor registers.

    This is one of the reasons that I have the sensor alarms set at 75 for a low now and 135 or 140 for a high, depending on the week. If the sensor tells me I’m high at 140 and alerts me to do a blood glucose reading, I will likely find out that I am really 180 – 200. At that point, I will treat the high and not be at all upset that the sensor never goes above 160 or so. It did its job. Similarly, if it warns me that I am 75 but I’m really 55 and hadn’t yet noticed, I don’t complain. I thank it for the warning. Of course, the low warning is less likely to tell me anything I didn’t know because I can feel the lows much more easily. Highs just make me tired and only in the 160-180 range. Below or above and I feel nothing.

  33. STACY KW says:

    Thanks –

    I’m happy to say that I’ve had much better luck with the sensors in the last week or so than I did at the beginning. And everyone is right… it’s all about calibration. And even though I’m still a little disappointed that it wasn’t going to work the magic I thought it would, it is better to have the trends and now that my trends typically follow the real deal, I’m much happier.

    Ivy, thanks for the offer of the cable for downloading the info from the pump but I actually have one now. I was given the phone number for SanVita, the company that took over making the BD test strips, and they sent me one… for free! Their number is 866-668-2629. Website is but I didn’t find anything about the cable there.

    Thanks for the all the advice.

    Stacy W

  34. Marnie says:

    I have been on the CGM now for 3 months…….. All the problems and errors you get in the first couple months are frustrating, but it is a learning process….stay with it. The CGM has gotten me up at night with a couple of lows…which was fantastic. I have little cousin who is 5 years old that got diagnosed with diabetes this last summer, she is pumping since this fall and just started the CGM this last month. Her and her parents are doing great with both…she is very slender and uses her butt for both the pump and the sensor. Less scary that way for her too. But she is a trooper….

    Anyways remember this doesn’t replace blood tests because it has a 20 minute lag time. It is to show you trends — and to catch the highs and the lows usually before you would catch them…. which Scott stated above.

    Thank you Scott for the site…

  35. Staci says:

    Just got my A1c and lowest in years with the CGMS at 6.7.
    So thrilled and my doctor is too. I love knowing the trends. It’s not always perfect but reflective of my bs anf after testing make adjustment as needed. Thrilled.


  36. Misanthropic Scott says:

    Marnie. You’re welcome. I enjoy feeling that this is helping others. And, it has helped me as well. This is difficult technology to use with a long learning curve.

    Staci, Congratulations!! That’s great news. As I’m sure you know, every little bit of A1C reduction helps tremendously with long term reduction in complications. Setting a new record low is definitely cause for a celebration.

  37. Craig says:

    I just wanted to say “Thank you” to Scott and all of the others that have posted here. I’m on my second day of using the CGMS, and I’m still trying to figure SO many things out. Everyone’s input has helped me out tremendously!

    I am still trying to really understand isig’s, though. Today, for most of the morning, afternoon , and evening, my isig’s were 10 or less, and my pump was telling me that I was below 40 mg/dL. My meter confimed that I was not low, and it seemed that no amount of moving/massaging would bring the isig’s and correct sensor readings back. Then, just a few minutes ago, my pump gave me a high level alarm. Doubting it, I checked with my meter, and it was within 3 points (and my isig was 15) — after being 100-150 points off for most of the day. The only thing that I did differently in the past hour was have a rum & diet Coke. I would imagine it’s just a dumb coincidence, but does anyone know if isig’s are affected by alcohol? Probably a dumb question…

    Also, does placing the sensor on a fattier part of the body (my stomach) as opposed to a leaner spot (my leg) compromise the quality of my isig’s? Sorry for the long-winded post, but I’m glad to find a helpful site.


  38. Craig,

    I’m glad this has been helpful so far. I imagine with respect to your isig issue, there is a lot of individual variation. Personally, I drink fairly frequently and have not noticed any correlation between isigs and alcohol.

    I have, however, noticed a lot of variation depending on whether I’m sitting around or mobile, especially since I still use a butt cheek for my sensor site.

    As for the high alarm after the low indication, I would guess that you probably did calibrate while the isigs were way off. That is something you will want to avoid at all costs in the future. If I’m correct, and you did calibrate at that time, what happened was that you told it that an isig of about 8 meant 100. Then when the isigs returned to 15, it assumed that your glucose had changed accordingly, which was obviously not the case.

    I can’t really say what exactly to do about getting your interstitial fluids flowing, which is what keeps your isigs good. I suspect that through pain and trial and error, you will start to magically just pick good places without even thinking about it so much. The brain is a great pattern recognition device. Stick with it. It takes a while.

    Until then, if that site cannot be calibrated correctly and maintain good isigs, you’ll have to remove it and try another location. I’d keep trying a while longer before wasting the sensor though. Calibrate only when the isigs seem reasonable. 8 may or may not be reasonable. If your blood glucose is 70 or so, it could be fine for some sensors. There’s a lot of variability in sensor and site with respect to the isig range.

    I have also found some sites just go through an hour or three with bad isigs and then get back to normal, usually due to activity, but sometimes for no apparent reason. Just remember, this is not life sustaining. If the isigs are bad, ignore the alarm to calibrate. You won’t get readings until you calibrate again, but when the isigs get back to normal, wait a little longer for them to settle down then calibrate and you’ll get much better readings.

    Lately, on most good days, I’ve been able to get the readings within single digits of my BG reading, at least when my glucose level is relatively stable or slowly changing. When rapidly changing, all you can hope for is directionality of movement.

    And, never worry about verbose posts on my site. You’d have to work hard to beat me.

    Good luck!!

  39. Staci says:

    My magic number so far for sensor use has been 7 days. After that the isigs start getting low and the numbers get erratic. So I feel lucky to stretch that far although other folks have written 10-19 days.


  40. Since I’ve read that others here have stretched so far on the sensor, I’ve tried that as well. I get about 7 or 8 days too. Then the ISIGs get low as Staci has found. And, the battery in the transmitter needs charging by then anyway.

    Has anyone ever seen the transmitter battery listed as anything other than good? I saw good right up until it died completely once. I missed what it was saying this morning before it died. But, the transmitter battery good message seems meaningless to me. Yes. It’s good. It’s completely drained of its charge and needs to be recharged desperately, but the battery is good.

  41. Staci says:

    How long does the transmitter last? If I received mine in December what is the time frame? Hate to be away and have it go down the tubes. Thanks..

  42. Staci,

    I’m not sure. I think they predict it will last quite a while, probably more than a year. However, ALL rechargeable batteries have “memory” despite manufacturer claims to the contrary. The best thing you can do for it would be to let the battery die completely every time before recharging it and always recharge it fully.

    Unfortunately, they do not make that convenient.

    It would mean recharging it at a time completely separate from changing the sensor. I am hoping that I can play around with getting my sensors to last as long as a battery charge. This may be possible for me. I think my transmitter battery dies much faster because my office has so much microwave interference that I continually get weak signal messages. I think this causes the transmitter to work harder, but am not really sure.

    One option, if you can afford it, would be to buy a second transmitter. I’m considering doing this. I believe that if I could switch them whenever the battery died and then charge the newly dead battery, both transmitters would probably last more than twice as long as a single transmitter.

    I do this with cell phone batteries and they often last me three years. When I didn’t do it with one phone, the battery failed to hold its charge after less than one year.

    I think the battery will most likely be the cause of replacement for the sensors.

    I actually do have two of everything I consider necessary for survival since I travel to fairly remote locations. I have two meters, two insulin pumps, etc. I do NOT have two transmitters. I personally think that after living for 20 years with diabetes without this device, if it dies on travel, I will simply live without it for a week or two or three.

  43. Has anyone out there tried this?

    Sometimes when my blood sugar is outside of my target range, but not far out, if my pump wants a BG reading, I lie.

    This sounds like a bad idea. However, after noticing that when I correct my blood sugar, the sensor does not register the full amplitude of my high or low, I have begun to make use of the knowledge.

    I would not do this with a blood sugar over 200 or under 60.

    Here are two examples of when I may do this.

    1) My blood sugar is around 150-160. My sensor wants a BG reading. I tell it my blood sugar is 10 points lower and take insulin to come back to my target range. Knowing that if I simply corrected the 150 reading, the sensor would never register as high as 150, but would likely only go as high as 140 or so, I tell it 140 instead of 150.

    2) My blood sugar is 60. My sensor wants a BG reading. I tell it my blood sugar is 10 points higher and eat glucose tablets (not something slow acting) to come back to my target range. Knowing that if I simply corrected the 60 reading, the sensor would never register as low as 60, but would likely only go as low as 70 or so, I tell it 70 instead of 60.

    I should stress that this is never as good as calibrating when stable and in the 80-120 range. It is also not anything recommended by Minimed. I thought of this all on my own and do not do it often. It works better than giving it the real reading for me, but not nearly as well as waiting until I stabilize between 80-120.

    I tend to do this if I’m at some party or something and really want use of the sensor for the unusual situation, but can’t wait to stabilize.

    Let me know if you have tried this and found it useful.

    If you try it because of my suggestion, just be warned that it will not be as good as following my original instructions above. The readings it gives afterward will likely be off a bit more than usual. I think it can keep them closer than giving the honest reading though. For me, the honest reading entered immediately before correcting either way throws the sensor off a lot.

  44. STACY KW says:

    Hi Scott –

    I have not tried the above idea although I understand what you’re trying to do. Hope it proves useful.

    Have you received the new BG meter from MM yet? (The One Touch.) I just got it last week. I didn’t link my old BG meter to my pump/CGM b/c it automatically used the BG result from the meter to calibrate the sensor whether I wanted it to or not. I thought they were going to fix this issue with the new meter, but it doesn’t seem like they have. Have you tried it yet? Is there a way around this other than NOT linking the two devices and manually dialing in the BG result?


    Stacy KW

  45. Hi Stacy,

    Yes. I received it. It’s too much larger than my Freestyle Flash and I’ve found the Freestyle too accurate to give all of that up for a bit of convenience in entering numbers. I tried the old BD when I first got the Paradigm and was horribly disappointed with the results. It took me a while to figure out how consistently it read higher than my actual blood glucose causing me ridiculous lows that were not accurately reported by the meter. I’m not giving up on Medisense (now therasense) for a long time. They were great when I got my first exactech. They’re still great.

  46. james says:

    Hey Scott – just reading some of your new comments and my thanks again for a great discussion. As mentioned in your other post I’ve been on the Guardian since November. I haven’t found too many other blogs detailing tips and tricks from experienced users so my thanks and well done.

    I wear mine almost constantly now and if I’m off for day or two find myself looking down for by BG numbers and missing it.

    The only time I’ve lied about my calibrations is if it hits the 3 day expiration and I’m out and about without my meter. I just restart it at whatever number it ended at. I use the Minilink blood sugar monitor which sends every reading to my pump. I haven’t had any problems calibrating with a low ISIG number – but then again I don’t take too many BGs when I’m low – since I know I’m low and don’t care to waste strips.

    I don’t have any new hacks to add – except I’ve been very surprised at how long some of my sensors have been lasting and providing accurate results when properly calibrated. I’ve had a couple sensors that have lost it after a few days, and a few I’ve completely screwed up after going in the hot tub. That’s a fun way to get some wildly inaccurate numbers.

    Also my transmitter battery field too has always listed it as “good.” My signal went out last night after a week of use. (listed as good up until that.) I took it off (the x’mitter,) charged it up, retaped it to my sensor and restarted it this morning. (As it was late and I was going to bed and didn’t want to be woken up by my 3-5 hour calibration.) As of today its still working great with accurate numbers. 8 days know so not too bad!

    Oh – a taping trick: I use Walgreens adhesive tape and for a while was just layering it sideways across the sensor/x’mitter. I now form an X shape across it. The width of the tape just about covers the width of the x’mitter, and making a nice long X holds it in place and uses less tape than several sideways pieces.

    All the best — James…

    All the best – james…

  47. james says:

    Oops I typed that twice. Here’s a question: Any knowledge on using the sensors after their expiration date?

    A few months ago I ordered a box of 10. Medtronic sent me THREE boxes of 10 – so I have three full boxes sitting in my fridge. At the rate I’m going (one sensor ever 8-10 days) I won’t get through them by their July 28 expiration date.

    Medtronic never called me back on the order and said the order WAS for 3 boxes (duh – that’s what was sent to it was obviously placed wrong,) and apparently my insurance has been covering these with a pretty good co-pay so maybe I could offer a box to someone reading this who uses them more sparingly or has less than stellar insurance and could use them up faster than myself.

  48. Hi James,

    I’ve been using 3M Gentle Paper tape for taping. I only started taping the transmitter recently because I didn’t want glue stuck to it. The tape is sticky enough to stay on for a week, but breathes nicely and does not leave glue residue behind. Of course, I still can’t figure out why they don’t just make the sensors with enough tape, If they were taped the way that silhouette infusion sets are, there’d be no discussion about additional tape.

    As for the expiration date, I have no clue. I would certainly try them and see how they work as they get older. In general, things of this nature after they expire will simply fail to work. They will not hurt you. That’s my NON-MEDICAL opinion.

    I would obviously suggest making sure they stay properly refrigerated until you use them. That’s sort of a no-brainer though.

    Please stop back and write your findings when you find out how long after the expiration date they continue to work. I’m sure I’m not the only one who’ll be interested in the results.

  49. Ivan says:

    I have spent 1,5 years to analyze what is continuous glucose monitoring system doing. It is not allways in line with Medtronic documentation and there are things you have to be careful. For more details visit

    [ed. note: fixed link.]

  50. Ivan,

    Thank you very much for sharing. Your site is excellent. I strongly recommend that everyone go to Ivan’s website for a highly scientific analysis of the continuous glucose metering system.

    Please be forewarned, Ivan is in Europe and is using European standards for glucose measurement as well as for time and date. Anyone that can handle the initial learning curve of the CGM system should have no trouble following that. He has listed conversions for the glucose levels on his site.

    Of particular interest to me, was a graphic demonstration of what I had learned intuitively, namely that the amplitude of blood glucose is far greater than the amplitude of interstitial glucose, meaning that the sensor will not read as high or as low as your glucose meter. This is diagrammed in detail on the page titled, “Blood and interstitial fluid glucose profiles”.

    Anyway, this site is such a must read that I will send out an email to everyone who has commented on this site in case anyone does not check back.

  51. Mary says:

    Scott and Ivan, thank you so much for sharing your knowledge and experience with this gizmo. I have been able to get over 20 days per sensor consistently for the last 2 months by following your advice. On a couple of occasions the insertion site was a little red, but other than that I’ve had no problems. And my experience is exactly like yours Ivan, that it takes at least 24 hours for the sensor to report accurately. So for the 20-day excursion I restart every 3 days and recharge the sensor on the seventh day. Once I forgot to recharge and the sensor died, but after recharging the transmitter I was able to restart the sensor and continue using it.

    So thanks again!

  52. Curtis Cruz says:

    Hi Scott,

    Thank you for sharing your knowledge on the usage of the CGM. Of particular interest to me has been your whole discussion on ISIG and what it all really means. I especially would like to thank Ivan for his technical compilation on this entire ISIG business. It really put things into perspective.

    Reading your site has really given me a head start in using the CGM. I’ve been using the paradigm pump for 3 years now and just recently began using the CGM when my insurance began picking up the cost. I recently obtained an A1c reading of 6.7 prior to using the CGM and cannot wait to see what my reading will be 3 months from now.
    I’m a 40 year old male with diabetes since I was the age of 9. I’ve experienced complications ranging from triple bi-pass to laser eye surgery for diabetic retinopathy. I’ve been stable now for several years and it appears things are back to normal for me. I am hoping this device will give me that much more control.

    I do have one question though. Is it a good idea to refrigerate the sensors? I have never heard of this and was wondering if you could re-iterate any explanations on why this would be true. No one has explained to me that this should be done nor does it give any instructions to doing so on the box.

    Thanks everyone again for your responses. They have all helped!!!


  53. Curtis,

    Yes. I have been refrigerating the sensors. Previously, they were sent in an enormous styrofoam cooler with ice packs. I’m glad they’re not being so wasteful anymore, but would definitely continue to refrigerate the sensors from the time they arrive.

    Also, don’t forget to let them warm up before you open the plastic to avoid having water condense on them. This was told to me when I received my initial training for the sensor usage. Are they no longer saying this?

    Good luck. Expect to take another 3-6 months before you really settle down in your use of this technology. I’m still finding that I was over-correcting based on the alerts and the extra readings they were causing me to do.

    My latest is that I’m timing my boluses much earlier than I had been in order to reduce my spikes, especially after high carb meals.

    Good luck. Please check back and let us know anything you learn along the way.


  54. Staci says:

    A few weeks ago I inserted a new sensor all being ok initially. Reading were good after the initial calibration. The next day I am having pain in my abdomen area and I was not feeling well. After a few more hours I pulled it out and did not insert another till the next day. First time since Dec’07 this has happened and have not experienced it again. Odd. I thought I hit some nerve and didn’t know it. Anyone else experience this?
    Anyway..I am still loving it and still find it the best reflection of the bg activity in my body along with the meter.

  55. I’ve experienced similar pain, without the other bad feeling, at infusion sites that sounded the way you describe. Since I put the sensors in my butt cheeks and the infusion sites in my legs, I don’t often get that from sensors. I have had pain at the site, but not the feeling of hitting a nerve there.

    I don’t know exactly why, but abs really don’t work for me the way they seem to for everyone else in the known universe. My abs are very sensitive. And, I also wear backpacks with waste straps that would definitely cause pain or discomfort at the site if I used my abs.

    BTW, for the first time, I’ve got a sensor that has really outlasted the documented time. I think I’m on day 12 starting today. I had to recharge the transmitter battery 4 days ago. I’m starting to change to letting the battery die completely every time, which leaves me changing my sensor and charging the transmitter on different days. I do think the battery will likely be the death of the transmitter, so I’m trying to extend its life by always letting it discharge completely and always charging it fully. I know this makes a big difference with cell phone batteries, despite manufacturer claims to the contrary.

  56. Emma says:

    Scott, this stream of information has answered so many questions and created a whole lot more. Thank you!!

    I would like to ask a question of Ivan (or you may be able to answer it). How did he crack the password to open the raw data files for his pump? When I used the Guardian system the password was easy to solve and I was able to analyze my data in a number of ways not available in the Solutions software. Now I have the integrated pump it is not so easy… any advice welcome!


  57. Emma,

    Good question!! So far, I’ve only ever heard of uploading data to their site through a linked meter. This seems silly. I want to see the data myself. I don’t want to purchase a cable for the privilege of putting my data on their site.

    Unfortunately, I do not have an answer for you. I have not even uploaded my data to the minimed/metronic site. My brain works pretty well for pattern recognition. So, I’ve mostly just watched it myself without the long term graphs and such.

    You may have noticed that Ivan has an email address on his main page. I’d try emailing him. I obviously can’t guarantee that he’ll check back here. If you do get an answer, please post it here.

  58. Emma says:

    Thanks, don’t know how i missed that email the first time I looked.
    Will let you know if I have any luck!


  59. Ivan says:

    Hello Emma, Scott and anyone who is interested,

    The password to open the downloaded files is wolfGang
    If it does not work for you, you can send me a mail.


  60. Ivan says:

    Hello Curtis,

    I normally keep my sensors in the fridge. I would recommend to do so but I would like to share my experience from the last summer vacation. I carried the spare sensor with me for nearly a week. And it stayed in temperatures around 40 degrees of Celsius (110 of Fahrenheit) most of the time. I did not noticed any difference in neither behaiour nor life time of this “heated” sensor and regularly handled sensor from the fridge.


  61. Susan says:

    Can anyone suggest a tape for the sensor. I can’t seem to get mine to stay adhered.

  62. Hi Susan,

    I like 3M’s Nexcare Gentle Paper Tape. James, above, recommends Walgreen’s tape. I like the 1/2″ 3M tape. I make an X over the sensor then place a longer piece across the sensor and transmitter. The tape is not so sticky that it leaves glue on the sensor as the tape that the trainer left me with does. And, the 3M tape breathes nicely and holds through many showers. I’ve had my sensor on for about 10 or 11 days now and have only had to change the piece of tape across the sensor because I charged the battery.

    I have no idea why Minimed didn’t make the sensor’s tape more like the Silhouette infusion set. That would be a huge improvement. The front of the sensor is what has to counter the weight of the transmitter and that’s where the least tape is. Bad design, but easily corrected with tape.

    Good luck!

  63. To Scott,
    I just discovered this feed searching for trouble shooting tips. I have learned alot.
    I have tried many tapes to keep my silouette and sensor tapes put in the summer. I work outside in Tn. and the humidity or sweat rolls off of me and nothing would last over 24 hours.
    The best I found for the silouette infusion site is the 3M woond dressing Tegaderm 1625. It was given to me as part of the DCCT research study. I fold it in half and cut a sem-cirdle out of the middle shile leaving both sides of the paper covering the clear membrane/ tape. The hole is just big enough (nickle size) to closely surround the female connector on my belly.This allowed me to connedt the tubing over the tegaderm with out loosing holding power. Then apply the tegaderm and remove the top paper, I found that if I streched my skin before adhereing the tegaderm I avoided the bottom edge and corner from irritating my skin when I reached over my head. The side tape on the infusion set would always let go first so i wanted to expand the width to give more holding power. It would last 3+ days of heavy work & sweating.

    I tried the same tegaderm for the sensor site but they left off any tape on the front of the sensor to grab hold of with the tegaderm. I have figured out that they must have done this to allow bleeding to excaoe since the needle is more like 2 knives than a round needle. I ended up making a smaller hole that would cover as much tape and plastic as I could and still remover the electronics to charge. I then put a bandaid over the sender end to hold it down. THis worked well until the hot, humid and sweaty part of June. I guess the larger profile put more stress on the tape.

    Our local minimed rep. is wonderful and she sent me a new product to try that was the only thing that would work for a bodybuilder wearing the sensor.
    I have just started using it last week. It is a liquid gum type glue called Mastisol. It is really great. Water, sweat , soap, shampoo do not effect the holding power. It holds so good you have to use an oily based, not alcohol based remover to get it to release. I still have to use a piece of 3/4 in silk tape or bandaid to hold the sender down. It has been really interesting to feel and see the tape/bandaid releasing its hold as it gets too wet but the mastisol shows no sign of budging. I found out that Mini-med has it in their store. I use a q-tip to apply it to 1/2 of the the sticky part of the tape before i insert and remover the needle. Seems like you are not supposed to put the needle through the glue. I can see where it would hold the needle in or keep it from going all the way in. After removing the needle I remove the other half of the tape cover and use the q-tip to apply to my skin under that portion of the tape. If you spread it to big the sender gets stuck and is hard to remove to charge. To get it off I use a q-tip dipped in the remover and rub it around the edgees anover the top of the tape and gently flick at the edge untill it releases and rolls up and off. The mastisol removes completely leaving no stickiness. There is hardly any odor to either product. It is my favorite now.

  64. BBohan says:

    Maybe I am the only person who thinks that the Minimed 24 hour hotline is great, but I do. I have used them a great deal over the last 19 years with my pumps and for the last year with my sensor and have found them to be very very knowledgable and kind.
    Scott, I real appreciate your putting this site together and have learned a great deal while reading each and every entry this morning. I think that you are to be highly commended for doing this…I only wish I had thought of it first! Thank you for all that you do and for all of the different opinions and true user tips that you give to us and share with us.
    I, too, miss the diabetic trainers being diabetic. I realise that these people who are not diabetic, and heaven knows I would never wish it on them, know a great deal about their product, but think that the been there/done that message would be most helpful. Still, I am grateful for all of these devices.
    I will be checking in often now that I know that you are here. I, personally, do not know how to begin to tell you how much the sensor has helped me with my brittle diabetes. I have had only 3 reactions in the last year with the warnings of my sensor vs. multiple reactions in the 38 years before I had it. I have no complications and have been a diabetic for 39 years and have worked hard at it. The feeling of freedom while alone, because of the sensor warnings now, is just too wonderful…and my low reading is set at 95! I still had an unconsious episode at 85 because I just couldn’t react fast enough to take care of it.
    I wear my sensors for 9-12 days and remove the transmitter on day 7 to recharge.
    Good luck to you all and I think that we can all offer advice to one another since we all know what the feelings are which we are experiencing. Thanks for the space to do this.

  65. Type1 32years says:

    Hello. I found these posts helpful when I got my CGMS a couple months ago, and thought perhaps it was time for me to post my own observations.

    I like using the sensors because it allows me to see up/down trends and respond to blood sugar fluctutations much sooner than before.

    I find that my sensor readings follow my blood sugar trends but report less of a change than my measured blood sugar readings. This has certain ramifications that hinder the value of the low/high alarms. Ideally, I calibrate the sensor only when my BS is 120 or less. This makes the sensor more reliable for reporting low BS situations. If it is time to calibrate when my BS is 225, then I have to take care to fudge the calibration (report 200 rather than 225) so that my normal BS reading are not shifted upward from their true values. If I enter my true higher than narmal BS value, then my low BS is worthless the sensor will never report my BS being as low as it is.

    I fully agree with posts that encourage calibration only when your BS is stable. Otherwise, additional error creeps in that further erodes the dependability of the actual sensor values. My best results are to calibrate when my BS is stable and less than 125. In this scenario, I am very pleased with the results. (I set my high alarms lower than the actual desired BS alarm level to account for the sensor not reporting my BS being as high as it is – unless I unwittingly calibrate it at an elevated value.

    I find my transmitter battery lasts exactly 7 days. According to MM, the batery is lithium-polymer, so it ‘should’ not be particularly benificial to discharge it completely before recharging it. In fact, lithium batteries seem to like frequent charge cycles. However, as a practical matter, I run mine dead simply because I use my sensor sfor 7 days (or more).

    My speculation is that sensor life is a function of BS values. In that the sensor has a chemical reaction in response to the presence of sugar, higher BS values would deplete the avalable chemical sooner. Thsu, if your BS hovers around 300 you might get the specified 3 days of use while a BS hovering around 100 would last 3 times longer. That is no doubt why we can get 8-12 days of use, despite the 3 day spec that must take into account worst case usage. My experiance is that the sensors don’t quit after X days, but rather the ISIG drifts at an ever increasing rate resulting in increasingly inaccurate readings between calibrations and eventual calibration failures.

    In addition to sensor (interstitual fluid) sugar values lagging 15 minutes or so behind BS values, I have found at least one circumstance where they differ radically. I was sick, sitting on the throne doing what sick people do when I also vomited. Seconds later my alarm went off, and the sensor reported my BS was extremely low. This was quite disconcerting because treating a low BS would have been especially difficult under the circumstances. However, a finger prick showed that my BS was about 80. What I figured out was that my stomach muscles depleted the sugar in my abdomin where the sensor was, triggering the alarm. Interestingly, the 3hr BS graph showed an abrupt drop (into the 40’s) followed by a near recovery over the next 20 minutes.

    I have bumped my sensor against various things (chair, tabletop, doorway, etc.) and found that this often disrupts my readings temporarily due to ‘pistoning’. I have suggested to MM that they redesign the sensor so that the nose tips down slightly. I think this would prevent the sensor wires from being pull partially out when pressure occurs on the back of the transmitter.

    I have set my ‘lost sensor’ alarm for 10 minutes. This results in an alarm after two consequative missed readings, and gives me almost a half hour to correct the situation. Untfortunately, I can sleep through alarms for awhile and have problems loosing signal when I roll over in bed (sensor is in thigh) and the pump is opposite my body from the sensor. This has been a bit of an aggravation, since I experience a lost signal as many nights as not. The only other time I have problems is when I am using a 900MHz cordless phone, and the problem can be fixed by moving the pump so that it is right above the sensor while the phone is in use.

    If MM reads this, I suggest they:
    1) consider increasing the tranmitter power to reduse lost sensor alarms,
    2) add high/low BS alarm thresholds for situations when BS is changing rapidly. If my BS is stable I want an alarm at 70, but if it is dropping like a rock I want an alarm at 85.
    3) update the calibration algorithm so that it includes an expotential component ((ISIG^1.15)*CalFactor) so the sensor better tracks BS values from 50-350.

    Finally, Thanks for this forum, and allowing us to share our experiences.

  66. Tom Bird says:

    I have been a diabetic for 35 years and a pumper for 7. Just started the Minimed CBGM 2 weeks ago and have nothing to share but frustrations so far, so I won’t!!!
    Just to say THANKS for the site, I’ve just started reading and have learned a ton so far. I’ll continue to read and learn and will contribute when I can. I was about ready to pull this thing out and send it back until I found this site. I can’t thank you enough.
    Tom B

  67. casey freeman says:

    I’ve had my pump for about 2 months now. In a some ways I LOVE the sensor. I am not good about testing my bloodsugar regularly, so I wanted the sensor to keep me from doing that and to have a tighter control on my BS. I also live by myself, so I wanted something that would notify me when my BS was low (especially while sleeping). However, my BS was just now 44 but the sensor was reading 115. That is a HUGE discrepancy!! Doing all those steps you listed sounds insane and incredibly time consuming. I have a job & a life & I don’t have time or desire to do all of what you listed. I sorta feel like damned if I do and damned if I don’t. I guess maybe I have to suck it up a deal with it b/c it can be very helpful. In all honesty, I just don’t want to have diabetes anymore!

  68. Tom Bird,

    I’ve been quite unpleasantly surprised that Medtronic/MiniMed does not start a site like this one for general issues with continuous metering. It’s almost as if being prepared for the fact that this will be very difficult, but still worth it will turn off people. Perhaps they’d rather have dissatisfied customers than have customers who got what they expected, a technology in its infancy that if used properly can be very helpful, even though not 100% of the time, or for that matter even close.

    casey freeman,

    I hated the damn thing for about 3-6 months and have grown to find it among the most frustrating technologies I’ve ever loved.

    That may not make much sense. Let me explain. It is very difficult to get used to the way the thing behaves. It is very difficult to get past the very long learning curve during which you will likely test more than you ever have before. It is very difficult to deal with the problems in communication between the sensor and the pump whenever there is any radio frequency interference, etc., etc., etc.

    That said, we have a condition which can be life threatening and can definitely be quality of life threatening, if complications set in. For that reason, any tool we can get our grubby little paws on that may help to keep us in tight control is worth it’s weight in gold.

    So, sometimes I do not get warned about my blood sugar. Sometimes the reading is very far off from reality. Sometimes though it wakes me up in the middle of the night when my blood sugar drops dramatically and I don’t feel it enough to wake up. Sometimes it is tracking so well that I can go through an evening of binging and drinking and maintain tight control throughout.

    Stick with it a while longer if you can. I think you’ll come to have a love/hate relationship with it that is a lot more love than hate. Learn to recognize when it is behaving well and when it is misbehaving. Learn how to increase the former and decrease the latter.

    If it is tracking well today, perhaps you can trust it. If not, you’ll have to do more frequent readings, as you would if you did not have the device at all.

    So, my point is that, though it is a frustrating tool, it can be a very useful one. There are many such tools in our lives. Cell phones, automobiles, computers, etc. all come to mind. This one is more frustrating. True. This one also may have a much more important benefit.

  69. Rachelle says:

    SENSOR MATH! I got this directly from minimed rep when I called with a problem and it works:

    Blood Glucose number divided by Isig number must be in range of 1.5 to 20.

    If it is outside of this, you will get a call error! I don’t do this every time I calibrate, but if I get 1 error and I want to avoid a second one I do the math to be sure before the second cal. (So, Yes, if your Isig’s are to low, or high, you will get a cal error) I have found this to be a problem though as my Isig levels typically run around 6 or less(sometimes 3 or less when I am low) and find that it is best not to calibrate when my sugar is low-normal.

    I have been on CGM for nearly a year now. My first 8 months with it were great. My A1C went from upper 7’s to low 6’s within this timeframe. I have been having more and more problems with the sensor lately, I have received MANY replacement sensors from Minimed for this reason. It is strange that I can use this for 8 months and not have one call to minimed with a problem but now suddenly I am calling them almost daily! They keep trying to tell me that it is something I am doing wrong (couldn’t possibly be their product) but if I had no problems for 8 months I must have been doing something right. Still I must admit it is better than having no sensor at all. I only hope that the technology continues to improve and the Healh Assurance will accept one of my insurance appeals. Will I be on Medicare before they ever agree to pay for this?

  70. Staci says:

    Has anyone yet received the new MM transmitter that is definitely flatter than the previous model?
    Also yes it is a love hate relationship. But if the sensor is not working correctly it is because my calibration was bad. Yes a low calibration is better. If you calibrate high and you have bolused to adjust the calibration may not catch it.
    My health insurance has now approved my sensors and new transmitter. I am thrilled.

    I wear my transmitter and sensor on my hip just below my beltline. Works perfect there.

  71. Scott S says:

    Misanthropic Scott, et.

    Thanks for your input. Good info on ISIG calcs and extending transmitter life.

    My initial impression of the CGM is that the technology is far from mature, but as Misanthropic Scott has stated, it is worth the investment as it does provide helpful trending data and should improve over time.

    I view the technology sector and the medical sector as expert consultanting resources for patients and it is incombent upon each of us to use available information to make the best decisions for our personal health and lifestyle.

    I talk to Medtronic when there is no other data available and have told them (after receiving insufficient data from them set by policy) that they prioritize their revenue stream over their customers which is unfortunate since they seem to have a historically healthy R&D budget.

    Scott S.
    Type I: 48 yrs
    MM Paradigm: 3 yrs
    MM CGM: 10 days

  72. Tom C. says:

    This web site and forum are great ( Also Ivan’s).

    I have been on the pump since a couple of months after I was diagnosed (SEP 06) and on the CBGM for about ten days now.

    I see I am not alone in thinking that there is more to this than what my trainer (also a type 1 and using everything) could tell me. While she is nice, an RN, and a Diabetic for 33 years and has great control with the use of the technology, she could not go into depth about how it all work. (I am an anal retentive, ex 20 yr Army Airborne Infantryman, now a computer programmer, and a control freak.)

    I was just sitting here pulling everything from the csv into a FoxPro database (I still have not seen the access databases created by download, something to look for) and analyzing the data to see how it presents itself and see where I need to make adjustments to get really tight with everything I have now (pump and monitor).
    While doing this I noticed the conversion factor (for ISIG during calibration) decided to see if there was any information on the net about it and see it there are any tools to use out there other than MiniMed’s site.

    I found this site and read everything on this page. Thank you, thank you, thank you!

    I also concur, Doctors/Nurses are great, however, they are not the ones that live with this 24/7. I just found my first doctor (Enodo) that actually touched my pump, changed my settings, and put in the script for the continuous monitor for me.

    I just want to say thanks again for creating, maintaining, and sharing your information with me, the new and inexperienced in this technology and disease.

    Tom C.
    Age 40 (yes really old to be a new type I)
    Type 1: 2 yrs
    MM Pump: 2 yrs
    MM CBGM: 10th day

  73. Scott S says:

    Tom C,

    Congratulations–you are a lifetime member of a health conscious, technically enabled fraternity that gets to utilize cool hardware/SW that really can impart well being into your life. I sometimes inform people who want to traverse down a sympathy alley that I am very fortunate to be a diabetic rather than an individual of great mental or physical challenges and that if everyone lived their lives as a diabetic, most people would improve their health standard.

    Misanthropic Scott has phenomenally good numbers as I recall (A1c <6) while others struggle. I target perfect. Maintaining your HW settings has a trial n’ error component to it due to the many variables that impact BG levels, some more manageable than others.

    In sports you have those who are technicians and others who play by feel, both of whom can be successful. To me, managing diabetes has a similar parallel to it.

    Best Regards,
    Scott S.

  74. Scott S says:

    Correction to above posting.

    I target {A1c of <7, but sometmes struggle to to hit my} target perfect.

    Scott S.

  75. Scott S.,

    Keep up the good work. The extra effort will pay off. So far, I’m still below 6 on my A1C, typically 5.6 – 5.8. I’ve had diabetes for 20 years and have no complications yet. My eye doc can’t even tell I have diabetes yet. The eyes are what keep me working so hard, 60% reduction in retinopathy for those who maintain tight control, according to the DCCT. All other results showed 50% redux in complications. Let’s all keep that in mind and do our best, whatever that may be for each of us.

    Don’t let a few bad numbers get you down. I hit above 300 or below 40 every once in a while too. I’m guessing all of the type I diabetics here do so at least a few times a year. With the sensor, I often get the warning in advance and don’t let it get so bad. I’ve been finding the sensor fairly reliable about 85-90% of the time, which is a huge improvement over not having it. Every tool helps.

    Anyone have a good trick for long drives? That’s when I do my worst. The insulin doesn’t absorb when I don’t move around and the sensor often doesn’t work when I’m strapped into a seat for a couple of hours at a time too. I find it helps when I’m a passenger to tap my feet to the music. I always keep my infusion set in a thigh, so moving the leg helps.

  76. Classicsound says:


    Thank you so much for all the information provided here and the opportunity for people to share their experiences over the Medtronic CGMS system. I have been on the Medtronic CGMS for about 6 weeks. My officemate has the Freestyle system and I see certain advantages to both. Being a pumper, I think the Medtronic system is the best for me; I don’t need to carry anything more than I already do now.

    As for my background, I am type 1 for 31 years and a pumper for about 18 years. I am a motorhead keyboard player by hobby and an electrical engineer by trade, but I get tired of having to understand so much technology in every aspect of modern life. I thought I would share some of my observations for what it is worth:

    I am running the sensor in my upper butt area, as I have been doing softsets in my abdomen for so long, I couldn’t conceive putting another thing in there! Plus, if one wears the sensor for more than 3 days, how do you keep it 3″ away from a rotated set? I guess, I would have to change my side to side rotations. My biggest problem thus far has been WEAK SIGNAL. Lord help me, it goes off in the middle of the night and my wife hits me. On a bad night I get a low reservoir alarm, weak signal and low alarm all in one night! I am aware of the need to keep the transmitter and pump in almost a line of sight. So I am wearing bottoms with a pocket, but it is definitely constricting me in my sleeping positions.

    The biggest hassle I am having is when starting a new set. Almost every time, I get these weak signals during the initial start-up time. I even put the pump in my back pocket next to the sensor to try to make it work. Sometimes, I pull off the transmitter and recharge it again and that fixes it, even though it says battery good. I also keep my phone out of that side of my body. The funny thing is, once I get it working it seems fine for the rest of time. The other day I had to “Find Lost Sensor” and that seemed to clear it up. Does anyone have a general explanation of what the difference is between Find Lost Sensor and Reconnect old sensor? I have had episodes where it got Weak Signal after 2 days and I charged it and that fixed it and I have also had it die well before 7 days. I also question whether an overnight charge is actually a good thing. Does anyone know if the transmitter is turned off when it is sitting in the charger after charging or when it is NOT connected to a sensor? I am speculating that it runs itself down when leaving it in the charger.

    The ISIG discussion here is invaluable for us. I used to have my meter(s) automatically update the pump and now that I know that is a recipe for bad calibration, I have turned that off, but I do miss getting the reading into the pump database. Suddenly I am thinking maybe it’s time to give up on the huge fairly inaccurate BD testers and the giant Paradigm One Touch and go for a tiny One Touch or Freestyle. Again, shame on Minimed, all they have to do is put a “Use reading?” conditional in the Sensor S/W so I can know I logged the meter and can use it for bolus but choose not to use if for calibration. Generally, I am trying to calibrate at “normal”, stable bloodsugars and some days, it is just dead nuts on all day. I do have my absolute whacky numbers and I have learned the hard way not to bolus or eat M&Ms based on the sensor UNLESS I am keeping my eye on a trend down and it’s been behaving all day. I also agree that it often takes it a little while before it really “gets in its groove”, but once it is there, it is definitely useful.

    What I haven’t seen mentioned a lot of here, that I have experienced quite a few times, is where the pump alarms with low blood sugar and you see this crazy dive, you test and it’s really where it was before the dive. It’s like all of a sudden the sensor just goes offline for a while and if you wait it out it can run well again for several more days. So these are the things you learn a long the way.

    As for the sensor life, I have had one feel so painful that I ripped it out after 1.5 days and I have had another that lasted 9 days and then I took it out for fear it would become part of me!. As long as it doesn’t go unstable and stay unstable, I am leaving it in. but on this note, I just find that on Day 3, I get an alarm, “Sensor End” and I just hit “Start New Sensor”, it asked me for BS within 30 minutes and we are off again for another 3 days. I have also played most of the games mentioned here, telling the system it is finger stick cal level when you are just speculating because you can’t get to it right then. I also have pretty good luck trying to anticipate the slope when calibrating during a rise or fall and adding or subtracting some points based on where I can guess it will be in 15 minutes.

    For me I think the best thing about this system is that it changes behavior very quickly. I learned that my favorite cereal was spiking me up to 260, while Cheerios was only getting me to 180, but quickly I found that taking insulin ½ hour before meals was like I didn’t eat and didn’t bolus. Now I am frequently riding through most of a day at like 110 – all day. I am hoping my A1c will now get down in the 6’s. I could never achieve that without lots of lows. Even on days where I just can’t seem to get it in line, I can atleast get a feel for the BS stabilizing and then I know I can finally notch it back down to 100. I am also quite pleased with my basals and corrections. It turns out they were amazingly spot on.

    In the end, I am pleased with the concept and relatively pleased with the execution. If we could just get MiniMed to make a faceless pump that WiFi’d to the iPhone, I think I will have died and gone to heaven. I mean really – can’t we get a recipe database in a pump like Animas did? The only complaint I have with the Medtronic pump is the tiny unreadable screen. I have developed (not diabetic?) serious close up vision issues lately and this screen has got to go!


  77. Dan,

    Long post and thanks for the info. I’ll see what I can answer from your questions. Quotes from your post are in italics.

    I am running the sensor in my upper butt area, as I have been doing softsets in my abdomen for so long, I couldn’t conceive putting another thing in there! Plus, if one wears the sensor for more than 3 days, how do you keep it 3″ away from a rotated set?

    Similarly, I use my thighs for infusion sites and upper butt for sensors. I think sometimes they come out fairly close, but never so close that they cause problems. I think you’re probably doing well keeping them in separate areas this way.

    My biggest problem thus far has been WEAK SIGNAL.

    Mine too. I keep trying to get them to create a wire interface. I’m already connected to the pump bu the insulin tube. Being connected twice wouldn’t be much worse. I don’t have a problem with weak signal in bed, personally. I do not worry about line of sight between pump and transmitter. I just keep them close. Usually it’s fine. Have you considered whether you may have excessive microwave radiation near your bed? Do you have a wifi transmitter, cordless phone, or other electronic device nearby? Perhaps you could turn it off or unplug it at night.

    Cell phones, microwave ovens, cordless phones, especially my cordless headset at work, all interfere with my transmitter. I always keep the pump on the side of my body with the transmitter and my cell phone on the other side. Still, I get weak signal alerts often, especially in the office with so many other electronic devices.

    They picked one of the worst possible frequencies for the transmitter. All manner of stuff interferes. (As an aside, it’s a little scary that we’re so bathed in microwave radiation all day long. It can’t be healthy.)

    I hope anyone else with this problem will ask for a future request for enhancement to have a simple wire connection. Even without the signal problems, replacing a $1,000 transmitter every 9-24 months is going to get annoying fast. Mine is 1.5 years old and is starting to have odd issues with both the charger and the transmitter.

    The biggest hassle I am having is when starting a new set. Almost every time, I get these weak signals during the initial start-up time. I even put the pump in my back pocket next to the sensor to try to make it work. Sometimes, I pull off the transmitter and recharge it again and that fixes it, even though it says battery good.

    I haven’t seen this issue before. I can tell you that in my experience, the indicator for the transmitter battery is a total lie. The battery is good right up until total death. I’ve never seen it say anything other than “Transmtr Batt: Good”

    Does anyone have a general explanation of what the difference is between Find Lost Sensor and Reconnect old sensor?

    Not me. I only use start new sensor and find lost sensor. I haven’t found a use for reconnect old sensor.

    Does anyone know if the transmitter is turned off when it is sitting in the charger after charging or when it is NOT connected to a sensor? I am speculating that it runs itself down when leaving it in the charger.

    My understanding is that the transmitter is only transmitting when connected to a sensor or to the test plug. I could be mistaken.

    What I haven’t seen mentioned a lot of here, that I have experienced quite a few times, is where the pump alarms with low blood sugar and you see this crazy dive, you test and it’s really where it was before the dive. It’s like all of a sudden the sensor just goes offline for a while and if you wait it out it can run well again for several more days. So these are the things you learn a long the way.

    I tend to have similar issues when I’m sitting still for a long time, especially on long drives (nothing like being belted into a seat to keep one nearly motionless). This could be due to using buttocks instead of abdomens. Regardless of site though, it is important to have new interstitial fluid (the fluid under your skin that the sensor is testing) in the area by the sensor.

    Without new fluid, the interstitial fluid’s sugar level will drop in that area, despite your blood sugar being fine.

    You could try massaging the area around the sensor. Pull and push the skin to try to get the fluid flowing. I’ve had mixed results with that. Mostly, just wait it out. It is not an indicator that the sensor is bad, at least not necessarily. If it never comes back, it is bad. Calibration errors also do not necessarily mean the sensor is bad. Even “sensor bad” errors don’t necessarily mean the sensor is bad.

    I’ve had sensors recover from all of those. For sensor bad, I usually have to disconnect the transmitter for a while, turn off the sensor in the pump settings. Then turn on the sensor again some time later, reconnect the transmitter and start new sensor.

    As for the sensor life, I have had one feel so painful that I ripped it out after 1.5 days and I have had another that lasted 9 days and then I took it out for fear it would become part of me!

    My record was 15 days, while traveling in Belize. My readings were very stable with all of the exercise from hiking and paddling. Why does that matter?

    Interesting note from my doctor: The sensor will last longer (assuming it doesn’t get infected) when you have lower blood sugars. The reaction between the chemicals on the sensor and the sugar in your interstitial fluid happens faster at higher sugar levels. So, the chemical on the sensor lasts longer when your readings are lower.

    Do not take that as an advocate of consistent low blood sugar. You don’t want dementia in your old age. Frequent lows can cause that.

    For me I think the best thing about this system is that it changes behavior very quickly.

    I couldn’t agree more. I made a slight adjustment to my night time basal rate almost immediately and got a nearly flat line through most nights. I also started timing my insulin differently and better to avoid spikes. My A1C has improved slightly, but since it was usually below 6, there wasn’t that much room for improvement. What I think I do get though is much more consistent readings. They’ll never be perfect without a true artificial pancreas. But, I get less frequent and severe lows and less frequent and severe highs. This can only be good.

    Bottom line: The technology is not there yet. The learning curve is huge. And, it is most definitely worth the hassle!

    I think I’ve already called it the most annoying technology you’ll ever love. I still feel that way after a year and a half with it.

  78. Transmitter Battery Low

    Update!! I have started to get this message now. After a year and a half with the transmitter, this week, I have begun to see this message for the first time.

    I think it means that the transmitter battery is truly dying, i.e. not properly holding a charge. As yet, it is still working. However, here are some things I’ve noticed now:

    1) When I put the transmitter on the charger, I get four fast flashes then the light on the charger turns solid green. It stays that way indefinitely. I no longer know exactly when the transmitter is truly charged.

    2) I get weak signal possibly a bit more often. I’m not sure since I’ve always gotten it fairly frequently.

    3) Minimed help line has told me that when it is truly dead, the charger will display a red light.

    4) Minimed has also confirmed that the numbers I see are still valid readings, or at least as valid as they ever are. Currently, it is tracking quite closely with my meter.

    5) Though the message has now been displayed for several days, the transmitter is still giving me readings. So, I do not believe it to be indicative of current charge, but rather of current ability to hold a charge.

    I am not yet sure how much of the replacement will be covered under my insurance. It will probably be a variable by insurance plans anyway, so not too useful.

    I am also not sure if my insurance will cover it just because the prior one has died. They may only cover a new transmitter every N years. Since the warranty is only for a year (I think), they probably will cover it.

  79. John Smith says:

    How do you get the sensor in your butt area? Do you need someone else to do it for you, like your SO, or do you do it yourself? I just started on my MM722+CGM last week and was about to give up on the CGM until I read this blog. Thanks!

  80. Hi John,

    I get the sensor into an outer area of my butt cheek by myself. I try to find a spot I don’t sit on anyway, so it’s quite a bit toward the outside.

    I reach around with the far side hand (left hand for right cheek or right hand for left cheek), hold a bit of the skin with my other hand, and use the automatic inserter.

    I always insert so that the transmitter is pointed down. Since the transmitter has no glue to hold it, I don’t want it pointed up and always pulling down and pulling the sensor out.

    Then I make the asterisk pattern of tape over the whole deal. I put an X over the sensor, connect the transmitter, and put a longer piece of tape across the sensor and transmitter to complete the asterisk.

    I do all of this with 1/2″ thick 3M gentle paper tape.

    Also, I always wear the pump/receiver on my belt on the side with the sensor, meaning the distance between the two is typically just a few inches. I find the transmitter can work for longer distances, but not in a modern office with cell phones, cordless headsets, microwave ovens, WiFi, and many other sources of microwaves. I carry my own cell phone in the opposite pocket to reduce interference.

    Feel free to ask about any additional issues. I’ve been using the sensors now for almost 2 years. They are still far from perfect, but have become a very valuable tool in my diabetes toolkit.

  81. Hi John,

    I should add that there is actually a pretty good reason that MiniMed/Medtronic recommends the abdomen. They feel that the interstitial fluid there flows more regularly. Using a buttock does have its downside.

    When sitting for long periods of time, the reading slowly drops, even if my blood sugar does not.

    This is not a problem in the office where I get up quite frequently. However, on long car rides where I am literally strapped into a seat, my blood sugar is often on the rise because my insulin is not absorbing as well at the same time that my sensor is showing a drop because my interstitial fluid is not flowing.

    Knowing this helps to deal with both conditions.

    Getting out and walking around a bit will help, as will just moving around in your seat and massaging both the sensor area and the infusion site. Tapping legs to the music helps with the infusion site as well, but not necessarily the sensor site.

    Good luck and feel free to stay in touch.

  82. Bob Maloney says:

    I have been on MM722+Cgm since November 2006. I am totally addicted to the system. Although, I have experienced many of the problems discussed above, the information provided has far outweighed any inconvenience. I have just discovered this site and have picked up some great info. Thanks! The system has reduced my A1C from 7.5 to 6.0, and I haven’t been a regular in the emergency room due to insulin reactions anymore. I feel like that with diet and excercise I can get my A1C in the 5’s. Info gained on this site will also help. I’m 60 yrs old and have been type 1 for 30 yrs.

  83. Steve Z says:

    I have been on the pump since March 2007 and using the sensor since Oct 2007. Most the info here is good. There is a steep learning curve to using the sensor. I had many frustrating days trying to figure the ting out but have pretty much mastered it now.

    One key is that you cannot substitute the sensor readings for meter readings. Even though my sensor readings are close to my actual meter readings for the most part most of the time, the sensor really should be used as a guide to where your BS is and where it is trending. Trending is the key word.

    I do not refrigerate my sensors, they are kept in a cabinet where it does not get warm. Medtronic has even stated that they do not need to be refrigerated.

    I have used sensors 2 months past their expiration dates with no problems. They work fine.

    I use sensors for 6 days (one charge cycle for the 6 days). I do not keep the sensor in longer than 6 days due to chance of increased scarring causing possible sensor problems in the future. Plus I start getting irritated at the site after 6 days. MY 6 day count starts from the time I initialize the sensor, not when I insert it…see next point.

    To combat the “sensor errors” and stabilize the sensor readings quicker into the sensor life, I insert a sensor and leave it in AT LEAST 6 hours prior to attaching the transmitter. This gives the sensor time to get wet enough to be stable. This was probably the single most helpful thing I found to my success with the sensors. This coupled along with calibrating when BS is stable gives me a reliable sensor reading 95% of the time.

    Occasionally I will get “weak signal” alarms that are not caused by RF. I have found 4 variables other than RF to cause these. Low transmitter battery, low pump battery, or faulty sensor, or just a bad sensor site (which could be caused by scar tissue among other things). I once had an entire box of faulty sensors. The lot HAD to have been bad. Once I switched to a new lot # the problem went away. I got a weak signal to go away by slightly pressing on the sensor site – hence the bad sensor site. Medtronic once told me that a “juicy” spot (aka fatter spot) on my body was better to use. The ONLY RF problem I have ever have in in a Chuck E Cheese with all those games in there.

    I pretty much stopped calling the 24/7 Medtronic helpline a while ago. I think, wait -no – I KNOW more than they do about how these sensors work (through all my trial and error). I have found a few of them helpful but most others I think are reading off canned information rather than LISTENING to my particular problem and helping me. In my humble opinion they are as useful as an umbrella in a hurricane.

    No matter what Medtronic says, the ISIG values is directly related to what your BS value is and a higher ISIG = a higher BS value and vice versa. When they say that a BS can be raising when ISIG in going down is a crock. Since 2007 that has never happened once to me. Not once. Speaking of ISIG, generally speaking an ISIG of 10 is a BS of about 100 for me give or take a little. It has always worked out to that.

    One last thing, before the sensor is going to “end” if you calibrate and then immediately “start new sensor” you will only be without a sensor reading for 15 minutes. Then the next calibration will be in 6 hours.

    • M Levine says:

      I’m about 30 days into using the pump and 20 days with the CGM. What is the sequence to using the CGM sensor past the 3 days?

      • M Levine,

        Sensor->Sensor Start->New Sensor

        This will reset the time to allow you to continue to use the sensor. I generally follow this with

        Sensor->Sensor Start->Find Lost Sensor

        This allows me to enter a BG reading immediately (even if it warns me that it isn’t ready yet) and it will be used, which is not necessarily the case after using the New Sensor option.

  84. Steve Z says:

    I forgot to add to my post above that since I started on the pump and sensor my H1C as gone from about 7 to 5.6

  85. Steve Z,

    Thanks for sharing a wealth of good information. I agree about the ISIGs, as well as about their 24 hour support team.

    When I started pumping in 1998, the trainers were themselves diabetics on the pump. They were extremely helpful for all but one situation.

    Now, it seems that the support staff and even the trainers for the CGM don’t use it themselves and don’t really have good answers for a lot of the situations. Combining that with the far less reliable system makes for some pretty bad support on their side.

    Still though, it is a good tool to add for better control, as evidenced by your own A1C reduction.

    Congratulations on getting such an amazing improvement.

    One thing my doctor likes to warn me about though, since my A1C is similar, is that frequent lows can cause dementia later in life. So, if you don’t already have it set to a fairly high number, you may want to set your low BG warning to something like 70 or 75. The 15-20 minute lag means that you need that warning at such a high level to tell you to check your BG.

    If my BG is dropping rapidly, I get the warning at 75 when my BG is in the high 50s. If I set the number lower, say 60 or 65, I wouldn’t get the warning until I was below 50. According to my doctor, an endocrinologist specializing in diabetes, frequent lows in the 50 range are what cause dementia later in life. I doubt any of us want that.

    • Steve Z says:

      I am familiar with the claim about the low blood sugars and dementia. A guy I work with has diabetes and goes to the Joslin Diabetes Center in Syracuse NY. He inquired about this with his Dr. and was told that the study that gave these results was done on an older group of type 2 diabetics that were in an age group that is susceptible to dementia to begin with. The Dr. put no credit behind the claim and also said to really prove that claim a study would need to be done on type 1 children and they would have to be followed through their life to monitor their cognitive ability. He said you’d lose more brain cells drinking.

      Having said this, it’s always a good idea not to have a lot of low blood sugars. I just wanted to point out this out.

      • Thanks Steve. That’s good to know that the dementia risk may not be real. I’m glad to have my mind a bit more at ease about the dementia as that is very worrisome. As you said though, low is still dangerous and to be avoided as much as possible.

  86. HarleyGuy says:

    Just found this site and just love the “real” info I have found. I am new with the Medtronic CGMS.
    One thing I am unclear on”Under sensor setup,review settings,missed data 0:40. Explain this to me please. Also,explain the “high” and “low” snooze. Also the “alarm” snooze, and whatthose times associated with the high and low snooze mean.

    I appreciate the time you have dedicated. It is certainly educational for this MM722+CGMS user.
    I thank you very much.

  87. Hi HarleyGuy,

    Missed data refers to what happens when the transmitter either needs to be charged or there is interference with the signal. For example, the cordless ear bud that I have for my phone at work is a powerful transmitter allowing me to walk around my entire office floor while talking. It always blocks the signal between the transmitter and pump, even when the two are 2-3 inches apart. The alert the pump will give for this is WEAK SIGNAL.

    The time on the setup screen is the time until the pump gives you the alert telling you about it. It is very important to note that this setting will not affect the amount of time before the pump gives up and says LOST SENSOR.

    I have mine set to 15 minutes (0:15).

    That way I have more time to try to do something to get the signal started again before losing the sensor completely and having to start calibration all over again. My action may be to hang up the phone or use the wire handset instead of the ear bud. Or, it may be to physically leave my office for a few minutes if the interference is from just the general level of radio waves in a modern office interfering.

    As for the high and low snooze times, when you receive an alert that your interstitial glucose is either high or low, you must acknowledge the alert. If you do not treat the high or low, unlikely with low, and it is still high (or low) some time later, it will alert you again. So, the snooze is the frequency with which it will alert you for sustained highs or lows.

    I have my high snooze set to an hour (1:00) and my low snooze set to a half hour (0:30).

    Good luck with the learning curve and the device. It takes a while to master, but is worth it. Don’t ever expect perfect results from it. It will never be perfect, but will be a very useful tool. And don’t forget to check Ivan’s site too.

    I happen to know he has some updates coming soon.

    • HarleyGuy says:

      Thank you so much Scott. Clear,precise, and to the point. Refresh me on “alarm snooze”.
      This is such a informative site. This is what us “newbies” need. I’ve been on CGMS 1 month today and have had very few problems. I read of so many Medtronic complaints, yet I have not had nearly a one, and that was my error anyway.
      I am just loving this technology.
      Thanks again.

  88. HarleyGuy says:

    As I thought it would be.
    Thanks for confirming my thoughts.

  89. Jeny-Lynn says:

    I have been using this system since November, almost a year, now, and have been diabetic for 32 years. Lantus or Levimar (along with many shots of short acting insulin with meals) did not work well for me, and going on a pump and continuous monitoring system has enabled me to lower my A1c value amost 2% after starting this system!! I attribute most of this success to being able to monitor my blood glucose continuously. I have encountered most of the problems mentioned on this web site, and have pretty much figured out most of the solutions that everyone has found to be helpful. I had a very good trainer, but, like all of you, she was not able to give me the information that we all have figured out on our own. One thing that she has taught me with this system, that none of you are using, is to cover the entire senor/transmitter with a transparent thin film I.V. Site Dressing by ReliaMed, 4″x4 3/4″. It is completely invisible and waterproof, and stays on in any kind of weather conditions. It is a little difficult to separate from the trasmitter after it has been removed, but with very gentle pulling, comes right off. I wear my sensors for 6 days, and it does not irritate my skin, which is very sensitive, or anything, and has a non-sensitizing adhesive. I order them with my regular pump supplies and my insurance pays for them. They come 50 to a box. I have not had any trouble with the transmitter catching on anything or the tape on the sensor coming loose. I would highly recommend trying it.

  90. Joanne says:

    Scott, you have helped me so much with your practical advice on CGM. After 7 months of frustration with inaccurate readings and cal errors, I was ready to throw the thing out. You’ve told me things my Minimed trainer, who is diabetic and on CGM, seemed not to know. I have more accurate readings now and very few cal errors, wearing the same sensor for 6 days at a time. Thanks!

  91. Bill says:

    The Site Dressing described above (by Reliamed) does not work while swimming. The Smith & Nephew one worked better than the Reliamed while underwater, but I have yet to find any good IV site dressing that lasts more than 10 minutes in the water. This results in the sensor dangling from its little adhesive, and ultimately cost me about half a dozen sensors.

    Anyone have good experience keeping the sensor against the skin while swimming?

    • Hi Bill,

      I don’t really have a great answer for that personally. Perhaps someone else does. I actually don’t swim that often. Here are two things to consider.

      1) I actually use my sensor in a buttock. So, unless I’m skinny dipping, the bathing suit helps hold it in place.

      2) Consider a large waterproof bandage, the type that is meant for larger wounds. That might help as it would cover the sensor completely. I believe BandAid, Curad, and 3M all make some version of this. Any bandage that is waterproof and large enough to completely cover the sensor may do the trick.

      Remember that your pump is not submersible, if it’s a MiniMed. They tried, but found that it works well in rain, but not for swimming. So, don’t keep the pump in the water with you.

      Good luck.

  92. Rebecca says:

    Scott, thank you so much for taking the time to post all this helpful information! I’ve been using the Guardian monitor from Medtronic for about a month now. I was having lots of trouble with the SG readings & BG readings being way off. I spent an hour on the phone with tech support and finally was given a formula to determine if it’s a good time to calibrate. First, she told me not to calibrate unless the isig is between .5-20 to begin with. If that’s the case, check the BG, divide it by the isig, and if the result is between 6-12, it’s good to calibrate. So far pretty good… But there have been times when the SG readings have been pretty stable, albeit a tad-bit high (between 140-180) and the isig is over 20. Do you think it is true that it would be better to wait until it is below 20? What experience have you had with this?
    Also, I want to see if I understood right: Is it good to store the sensors in the refrigerator?
    Also, what brand of tape do you recommend to secure the sensor?

  93. Hi Rebecca,

    Good luck and stick with it. The learning curve is a long one. You’ll never get it to be perfect. But, it can be very useful.

    That said, I don’t worry about ISIGs being too high, other than that it probably means either that the sensor is new and is reacting quickly with your interstitial glucose or that your interstitial glucose is high. (It’s likely that your blood glucose as well, in that case.)

    I find it best to calibrate when my blood sugar is stable. So, on the first day, I will usually wait ’til before meal time, when my BG is usually in the normal range, before giving it a calibration. If it is not a new sensor, I often check the graph of SG readings on my sensor to see if it’s relatively flat before calibrating.

    Either way, I have not noticed any issues with ISIGs being too high to calibrate other than that the first day ISIGs tend to drop relative to BG over the whole day. Sometimes, I try to anticipate this a bit by giving a slightly higher BG reading to the sensor than my meter actually says.

    I do often tell small lies to my sensor based on my own recognized behavior of it. For example, I know that the amplitude of the SG readings is usually lower than the BG readings, meaning that the sensor tells me I’m closer to 100 than I really am.

    So, if my BG is far away from 100 in one direction or the other and I must give it a reading anyway, I may tell the sensor that my BG was closer to 100 than it really is. I might say 74 instead of 70 or 145 instead of 155, or some such. If it’s very far off, I usually just try to get back in control before giving it any reading.

    Either way, I worry more about the stability of my reading than the ISIG value, especially with high ISIGs. High ISIGs in the absence of high BG indicate good interstitial flow and a new sensor. The only worry there is that as the sensor ages, the ISIGs will drop relative to BG.

    Low ISIGs likely mean low circulation to the sensor area or an older sensor. If the latter, replace it. If the former, try moving around a bit and/or massaging the area around the sensor to get fresh interstitial fluid to the sensor.

    As for tape, I like 3M Gentle Paper Tape. I buy half inch thick and place a diagonal X over the sensor prior to attaching the transmitter, leaving the back end open for the transmitter. Then I attach the transmitter and put a longer strip over the sensor and transmitter together, making the whole thing look like a bug or an asterisk. This tends to hold it well for a week.

    Lately, I’ve been changing it every Thursday. This gives me very little useful information on Thursday, which is a pretty normal work day for me without much diet and exercise variety, making the sensor less critical. Then it gives me a nice fresh working sensor for the weekend, when I need it most due to maximal variety in diet and exercise.

  94. Kelli says:

    Just found this site tonight, I just got started using the CGMS this week, although I have been a pump user for 12years now. I want to get better control, as over the years it seems as if female hormone issues have caused it to go crazy. Very helpful information, as I did not realize the sensor could be used longer than three days. I am wondering if anyone has had this come up with the weak signal though…which seems to be my only major problem for now. I seem to get a weak signal at bedtime in the bedroom, I first I thought it was my new iPad, but it must not be the only thing as tonight it did it before I used it. When I get the weak signal I don’t seem to be able to get it connected again and then after ten to twenty minutes the pump restarts the sensor and I have to go through the 2 hr waiting period again…

  95. Hi Kelli,

    Weak signal problems … welcome to my own personal hell with this device. As I’ve stated in the main article (specifically rule #2), I would much rather be tethered to the pump with a wire in addition to the tube than have the wireless communication of this device.

    Everything interferes with it. WiFi, cell phones, blue tooth, cordless phones, cordless headsets, microwave ovens, etc. The device designers used the single most overused frequency for the communication between the transmitter and the pump.

    During the day, wear your cell phone on the other side of your body from the pump. Always wear your pump as close as possible to the transmitter.

    Since your problem is in the evening, check around your room for anything wireless. Cordless phones, WiFi, cell phones, almost anything that uses microwave radio will interfere. Some devices will interfere even when not in use. Cell phones are always checking their signal. WiFi transmitters, unless unplugged, are always transmitting.

    Try moving all devices farther away. You may want to try them one at a time, so that you only move the ones that matter.

    For me, the problem is just being in a modern office during the day. We have wifi, cell phones, microwave ovens, cordless headsets (my own personal one is a guarantee of weak signal from the moment I start using it ’til the call ends), etc.

    Good luck. Let me know if any of this helps.

    Also, remember to use find lost sensor rather than start new sensor when you lose the signal. It should pick up where it left off, without having to recalibrate.

  96. Kelli says:

    Thanks for the info, the problem I have is the the pump actually restarts itself when the signal becomes weak. Like last night the signal was weak for no more than ten minutes when on it’s own it started the the start process again. I did not touch anything nor had a chance to even try to get the signal back by repositioning it. Again it did it this morning morning but after about 25 minutes. I have the alarm set to warn me after 20 minutes, but I think I need to change that to try to get ahead of the game. I am wondering if anyone has experienced it restarting on it’s own before the 40 minutes, I never even get a lost sensor alarm, because it never gets that far.

  97. Kelli,

    I had trouble with the missed data alarm being too late as well. I currently have that set to 15 minutes. That usually gives me time to take action.

    As for restarting on its own, that all sounds very odd. Mine gives me the lost sensor alert after warning me of weak signal. However, even after a lost sensor, I have to tell it to find lost sensor for it to restart. And, it usually picks up where it left off with the sensor already properly calibrated.

    So, no. I have not had that issue. I would suggest calling the 24 hour help line, though I’ve not been thrilled with their level of service. If you can verify that problem though, they may replace your pump. Unless I’m misunderstanding what you’re saying, that sounds like defective behavior.

  98. Marianne says:

    Have you heard of anyone having ringing in their ears since wearing the sensor? I may have tinutus but it started when I started wearing the sensor and seems to get better when I am not wearing a sensor. Weird huh?
    I wish the insertion needle was smaller and sharper also as well as wishing the sensor itself was smaller. Hopefully Medtronic will come out with an improved model soon!!!!

  99. Jeri Sehl says:

    OMG…wish we had found this site 1 1/2 years ago when my husband (Ed) started using a sensor. Not the most patient of men, the number of “cal errors” and “bad sensor” warnings has been enough to drive us both over the edge, nearly. Today he called the help line and someone told him about the ISIG value…first time anyone ever talked about that. So, I did a search and here you were!
    I’ve read some of the old posts….we never heard that the sensors should be refrigerated? Is that current information?
    Thanks for taking the time to do this!

  100. Jeri,

    I do not believe sensors still require refrigeration. That seems to have been the case when they were still largely made by hand in limited numbers. They used to ship them in a styrofoam cooler packed with ice packs.

    Now they do not do that anymore, thankfully for the environment.

    I did ask at some point though and they said it doesn’t hurt. So, I still do it in hopes of preserving them for longer. Just make sure that if you refrigerate them you let them warm up prior to opening to avoid condensation on them.

    Please also check out Ivan’s site.

    My site is more practical information; his is a much more scientific study. I highly recommend it.

    I can’t believe no one mentioned ISIG to you for a year and a half. It’s probably the most important thing about the sensor to understand if you want accurate readings.

  101. Marianne,

    Sorry for the slow reply. I have not heard anything about tinnitus from the sensor. I have mild ringing in my ears occasionally and have not noticed it being any worse since the sensor.

    I assume you are using the automatic inserter with the sensors, correct? I too wish they were sharper and thinner. I’m not sure what that would do regarding the amount of chemical they could coat it with and hence how long it might last.

  102. Steve says:

    Hello, I posted here back on 9/1 & 9/2/2009. You can read my history there rather than re-iterate it again in this post. I recently have started having issues inserting the sensors. I use the senserter (and have 3 of them and have tried all of them)…The sensor will not insert al the way, it maybe goes in 1/2 or 3/4 of the way and will not go in any farther even with trying to manually push it in the rest of the way (I try to not be too forcefull, if it doesn’t want to go I’m not going to just ram it in there). Has anyone else expierenced this? Is it my body or is there an issue with the needles?

    • Hi Steve,

      That’s a new one on me. Let’s see if anyone else answers. I do sometimes have issues with my infusion set, which I prefer to insert by hand, and sometimes switch to the sil-serter when I have trouble. But, not getting the needle all the way in from an inserter seems very odd.

      Have you been using the same location for a while? Perhaps the skin there is getting calloused. If not, then perhaps there is an issue with either the needles or the inserters (but three would be very odd).

      I would suggest trying a new location if you’re using the same spot repeatedly and hold the skin up a bit, but not pinched so tightly that it becomes taut. Then click.

      I hope this helps or at least gives you something new to try. I haven’t had the issue.

      • Steve says:

        I rotate locations on a regular basis. The areas I can’t get the sensor in fully is not used any more than other areas thta don’t have any problems. Maybe it is calloused or there is scar tissue under the skin in those areas. I am curious to see if anyone else has had the issue.

    • Nancy May says:

      Steve – I haven’t had as much experience as Scott has with the sensors, tho I’ve had them to use for > 2 yrs, but I have had the same issue as you. But differently than you, I do push the inserter needle further in manually so that the sensor platform rests on the skin surface. I’m pretty sure that the cause (for me) is that I flinch as I depress the inserter button, thereby pulling the blessed thing away from my body. I gave myself shots for 25 of my 35 yrs as diabetic, and have been a pumper for 10, but that long-assed inserter needle for the sensor STILL freaks me out. I’d suggest, as Scott has, that you rotate insertion sites, too. But for me, I know it’s because I pull out as I’m pushing in. You may ask a friend or companion to watch you?

  103. Dana Friedrickson says:

    Scott – Thank you so much for your should work for medtronic! I was a pump user 25 years ago when they were the size of a small television and the infusion sets were actually small gauge needles that stayed in post insertion. I experienced many problems from not receiving alarms to poor training. Now, being a “return pumper” for the past year, I am amazed at the technological advances, convenience and overall better health. You have given me many great tips on extended sensor usage, how to prevent cal errors, and most helpful for me is to watch the isig…this makes all the difference in the world. In using the pump my A1C has actually gone up to a 6.5 from a 5.8, which is what my physicians wanted. I had experienced too many lows resulting in seizures. Most importantly, no hospitalizations due to diabetes since I started the pump and real time. I was concerned however, with scuba diving and the pump. Once my physician gave clearance for the sport I was able to work around being “detached” for an hour a day by reconnecting and bolusing in my basal rate post BS check and going on two to three dives a day. Thanks again for your informational site!

    • I’m glad I could help Dana. Since posting this here, I have also learned a lot from those who left comments. If you haven’t already checked it out, please don’t miss the far more scientific site Ivan has been maintaining. His information is very different and more technical. It compliments this information well, IMHO.

  104. Steve says:

    I’m not sure if anyone has tried using sensors past their expiration dates so I wanted to share my experience. I have been using sensors that were 6 months and 1 year past their expiration dates and they work normally. There has been no issues with erroneous sensor data or site issues. They work as well as “new” sensors.

    Secondly I wanted to share a Medtronic “help line” story. I stopped calling them a long time ago because their advice comes in the form of canned responses that a 10 year old could give. Once my experience and knowledge surpassed theirs they became irreverent. Anyway I called to ask if there was any physical or biological reason to not use expired sensors. The person I spoke to told me she would type it into Google to find out! THAT is truly the LAST time I will ever call them for assistance.

  105. juliann says:

    I have learned so much, thank you. I wanted info about using sensors that had gone past their expiration date, so thank you Steve. I was told by Medtronic’s that the sensors have live enzymes that die after the expiration date so the sensors will not work. I am not going to throw them out now.

  106. Kim says:

    I am fairly new to the sensor and am really frustrated. I keep losing calibration without understanding what I am doing wrong…This morning I tried “18” and it was great for about 3 hours. Then, my sensor alarmed saying I was low, but bs was actually 200…….Can you help me with this?

  107. Kim says:

    ps… far as I know, I am stable when I calibrate and isig is okay…..

  108. Hi Kim,

    First, I don’t understand what you mean by ‘This morning I tried “18”‘. I assume you do not mean that you calibrated with a blood glucose of 18 mg/dL or 18 mmol/l.

    As for wide discrepancies between sensor values and blood glucose, there may be two causes. The most obvious is a rapid change in blood glucose where the interstitial fluid is behind the curve. However, your numbers sound beyond that possibility.

    Perhaps, even though the ISIG value was in range both times, the initial calibration was performed at a time when the calibration factor was much higher than it should have been later. This can be caused by insufficient circulation of interstitial fluid. You can try moving or massaging the body part in question to get the fluid flowing again.

    Remember, you can be stable but your interstitial fluid may be stagnant. If so, you will not get new fluid to test. Therefore the reading will slowly decline over time regardless of what your actual blood sugar is doing.

    This technology is a wonderful addition to your toolkit for monitoring your blood sugar but will not be accurate all of the time.

    Where you place the sensor can have a huge effect as well. I personally use my butt, which is not recommended. Abdomen is best. I just can’t put either the infusion set or the sensor there for other reasons (including pain and backpack waist straps).

    I hope this helps. I may be able to help more if you explain what trying 18 means.

    Also, don’t forget to check out Ivan’s site, which is far more technical than my own.

  109. Kim says:

    Hi Scott. Sorry for that last post ambiguity…I was frustrated and low sugar and forged onward when I really needed to just stop. Know the feeling?

    The “18” refers to the instructions you wrote in your post. On 19, you write to try 18….

    I was going to restart my old sensor this morning, with what my doc’s PA advises – to start stable, and then calibrate 4 times in one hour. But my sugar was 70. So I turned the sensor back off and hope to retry this afternoon.

    I would love to hear from you, and get your advice before I retry. The sensor is 1 day, 1 hour old. It is about 8am. I am going to try again at noon……

  110. Hi Kim,

    Sorry I was out all day.

    It has been a while since I reread my original post. In step 18, when I use find lost sensor after start new sensor, that step is actually not important. Starting the new sensor will do the same thing if you wait a few minutes until the next time the sensor transmits the value to the pump. At that time, the pump will recognize that you don’t need to wait the 2 hours. Either way, you can also just enter the blood glucose immediately. It will give you a warning that the value will not be used because it is not ready for a reading. But, then, it will use it anyway. At least that has been my experience of late.

    I’ve never heard about calibrating 4 times in an hour. Perhaps I’ll give that a try. I think if you do start new sensor and just give it one reading while stable, it will be fine though. Just remember that it will want the next reading within 6 hours instead of 12. That second reading can be given much sooner than 6 hours. Though, I usually do wait some time before giving it a second reading. I have not found it does anything to give it the same reading within 5 minutes, for example.

    Let me know how that 4 readings in an hour works. I’ll let you know if I decide to try it at any point.

  111. Bob says:

    Hi, Scott. Awesome website. Thanks!! I’ve really benefited from everyone’s advice. I’ve now had the sensor for over 6 months and love it. However, I’ll admit that it was very frustrating at first. I wanted to offer up a few things I’ve learned in the hopes that this might benefit someone out there:

    1. The first week or two are the most frustrating. Hang in there.

    2. My self serter does not always insert the sensor all the way. No big deal. I just manually push the sensor the rest of the way to get it flush against the skin. I don’t believe that this is due to scar tissue as I’m very careful about rotating insertion sites. I saw others asking about this issue.

    3. Turn the sensor off and then back on before calibrating if there is a huge discrepancy (like 50 points) between sensor and monitor. Off sourse you need to have a stable sugar (no arrows for example) before calibrating. I won’t say anymore since many people have already discussed this topic.

    4. Insert the sensor the night before you need to start it. This lets the new sensor get fully “wet” and reduces the number of erroneous values. I use the old sensor through the night and then move the transmitter from the old sensor to the new sensor first thing in the morning.

    5. Discrepancies between the sensor and my blood sugar monitor seem to be greatest the first day. Days 2, 3, 4, 5, and 6 seem give me better correlation between monitor and sensor.

    6. Values during exercise can be way off. If the values start trending down during exercise, the actual blood sugar may be far lower than what the sensor is reading. This is often the case.

    Thanks to all the contributors! Great community!

  112. Excellent info Bob! Thanks for sharing. I have only recently changed my focus from getting the most from each sensor and from the transmitter itself to getting the most medical help. To that end, I too have discovered that 6 days is correct and that inserting the sensor the night before is best. (Note: To protect the sensor that is not in service yet, I use my old dead transmitter to cap the end.)

    I have not tried the turn off and on method for recalibrating. Interesting thought. I usually just tell the pump that the sensor is new. Within 5 minutes, it wants the new reading. In fact, it will even take the reading with a warning message before then and still use it. But, this requires another reading within 6 hours rather than 12.

  113. breaddrink says:

    I’ve had my continuous glucose monitor for a few months now.
    I’m feeling fairly mixed with my opinion of it.
    Reading these messages has however been very helpful, combined with an unsettling sensation in my mind while reading about dividing glucose readings by the isig of “I know this is first generation, but shouldn’t it be a little easier (work better) than this?”.

    It’s taught me a lot about how my insulin reacts and although unreliable at times is showing me some daily trends that I somehow was missing due to being just so set in my ways.

    Does anyone have any direct comparison to the ping system? The few pages I’ve come across seems to have users having more accurate results, but as odd as it may seem in this context, I also think this may be borderline brand loyalty with those people and the investment they decided to go with…Again a little weirded out by this as it’s a medical device, not a PS3 vs Xbox, but whatever. I guess it’s to be expected.

    I’m not about to give up on it yet, and in fact when I don’t have one connected now I feel a little ‘naked’ and so I suppose this may say a lot in itself, but I’m also awaiting something a lot better.
    I’m prepared to jump ship to another company to get it too.

    Oh, one last thing…Do minimed accept real user input in how they might improve things? I mean, even really basic things seem to be pretty badly flawed (adhesive strip size and location considering sensor size and weight, for example).
    I understand earlier designs combined with product runs need to pay out before the next generation can begin, but there seems to be some really huge design flaws.

    This may be running a little long, but I’d also really love to hear opinions of the physical range between pump and sensor and why it seems to be so short.
    I’m a little surprised how short this distance has to be. It’s so short in fact that I wonder if it might be simpler to just connect the devices with a physical data tether and lose the wireless altogether. I don’t think people would be all that fond of remote controls for their TVs if you had to be 2 feet away to use them and what with it’s already slightly picky nature, I wonder if it’s simply adding to the negatives to have it wireless.

    In short, I like it, but I would recommend it with caution.

    So there I am. Just thought I’d chime in. Try not to shoot me please 🙂

    • Re: ping. I have no idea. However, I believe it is still based on testing interstitial fluid, which I don’t believe can ever be really accurate the way a blood test would be.

      Re: user input. I did complain initially about the enormous size of the original transmitter, as well as its price and battery life. It is better now. I don’t know how much my opinion counted.

      I also suggested a wire connection rather than a low reliability wireless connection. Clearly they didn’t like that. I see that you have the same opinion.

      I had been hoping that someone would implement this with blood testing. I contacted Animas about their continuous blood test. They never got back to me. I have not seen anything recent about this.

      Animas now s working with another company to use subcutaneous testing rather than blood testing. Perhaps we’ll never get an artificial pancreas. 25 years ago they told me it was ten years away. I think it still is. I don’t even think Minimed still makes the implantable pump to deliver insulin intravenously, which I also believe is important to avoid differing absorption rates due to activity levels.

      In short, I’ve become very obsessed with blood. I think the only ways to get to really good control, i.e. non-diabetic control, are 1) blood testing and intravenous delivery in a closed loop system or 2) stem cells and a biological solution.

      Minimed seems intent on selling supplies, the lion’s share of their cash flow. An implantable intravenous device would not be nearly as expensive (revenue generating) on a monthly basis. I think they make more this way and are happy about it.

      Maybe I’m just a cynical misanthrope. I have no real proof, of course.

      Still though, j’accuse.

  114. Bob says:

    Scott, can you share how you determine when a transmitter needs to be replaced? For example, do you get a new transmitter when the battery life hits a minimum? Or…do you notice the device giving you many “weak signal” warnings? Or something else?


  115. Bob,

    I’ve had to replace my transmitter just once so far due to the battery not holding the charge.

    See an earlier post of mine on this thread:

    Transmitter Battery Low

    Note that the only time I have ever seen the transmitter battery low message on the status screen is when the transmitter battery was no longer holding the charge. Support will not agree with this assessment. But, when you get that message, if you want to avoid a large gap in your sensors of about a month, get a new transmitter immediately. When this one dies, I intend to fight them tooth and nail if they claim that the message means anything other than the transmitter is dying … and soon.

    Oh, and please note that my current sensor is already older than my first one was at replacement. (Check the dates of my posts.) This despite the fact that my current sensor only ever held a charge for 7 days and the original held a charge for 9-12 days. So, even though the charge when new on my older one held for longer than my current one when new, I am still getting over 6 days and have not yet seen the transmitter battery low message. Strange.

    • Breaddrink says:

      I too have noticed that the battery strength is always at good. I get roughly 6 days out of mine before it starts telling me that signal strength is low.
      A charge at this point gets it up and running again, clearly showing me it’s the battery and not the sensor. I’ll get at least another 3-6 days from the sensor again after this second charge.

      I love how minimed stand by their product warranty when it’s clearly their fault, but I too have had issues where they will not admit to being at fault when they simply are.
      My first pump used to clear it’s entire memory when I changed a battery over to a fresh one, and they refused to admit that this was a fault.
      Every pump since then hasn’t done it.

      This stuff is expensive and I find it a little disrespectful to be treated in this manner.

  116. Steve Z says:

    I used my first transmitter for 2 1/2 years before I got a new second one. It was not dead or dying…my insurance will pay for another one if it’s outside its warranty period and there is something wrong with it or if there are any cracks etc. It had one mark on it which looked like a hairline crack so it was covered, plus I wanted a backup. I’ve been on the second transmitter for 1 year now with no problems with it at all. I believe the trick to longevity is to completely or almost completely drain the battery before recharging it. I use one sensor for 6 days. In testing the transmitter battery life I let it go as long as it would on a few occasions and I found that the charge lasts aprox 7 days. When the transmitter battery is dead after those 7 days I get the weak signal/lost transmitter messages. There is no battery low message that ever comes up. In 3 & 1/2 years I have NEVER seen that message which lends credence to your experience Scott. Medtronic support is the absolute pits. They do not have no clue about how their equipment actually operates out here in the real world. I posted on here a while back that I called support to ask if there was any physical or biological reason to not use expired sensors. The person I spoke to told me she would type it into Google to find out! Enough said.

  117. Steve,

    As I posted here long ago, I am a firm believer in letting batteries die completely before recharging them. That said, I did that 100% of the time with my first transmitter that died in 1.5 years. I have stopped doing that with my current one after deciding that I’d rather have more accurate readings more of the time than have the transmitter last forever, which it won’t anyway. And now, this one is older than the prior one ever got.

    Strange. I have no explanation for that.

    • Michael says:

      Nickel-cadmium batteries last longest when fully discharged before recharging, as they have ‘memory effect’. Ni-Cads tend to charge from the end of the last usage rather than from the initial charge.
      Lithium-ion batteries have no ‘memory effect’, but do tend to perform better if recharged prior to full exhaustion and will recharge faster if recharged more often.
      I do not know what batteries Medtronic uses or has used. But the type of battery may be the reason for the differences.

      I believe that, “As long as there is so much money to be made in selling relief for the symptoms of the common cold, there will be no cure.”

  118. Steve Z says:

    More accurate readings? How do you mean? I have always let my battery run down and I haven’t experienced inaccurate readings.

  119. Steve,

    I probably wasn’t all that clear. I mean accurate readings a greater percentage of the time. When I change my sensors every 6 days, I get more accurate readings than trying to squeeze every bit of life out of them.

    Similarly, when I charge my transmitter at the same time as I do a sensor change, I don’t end up missing a chunk of a perfectly good day during mid-sensor life by taking the transmitter off to charge it then having to wait 2 hours to begin getting readings again.

    This is all part of the change I made that also includes inserting the sensor the night before and putting my old dead transmitter on it to protect it.

    In the morning, I then take out the old sensor, charge the transmitter, shower with the new sensor still having the dead transmitter protecting it.

    When I come out, I put the freshly charged and working transmitter on the new sensor and begin getting reasonably accurate readings in 2 hours with a sensor that is now well primed by having been inserted for around 12 hours.

    This is the only time I really have to live without the sensor giving decent readings now, except for long car rides or other situations where the damn thing simply doesn’t work properly because subcutaneous fluids simply are not as good for testing as blood.

    • Steve Z says:

      I do the same thing (pretty much) as you do with putting in a new sensor the night before etc and only miss a 2 hour block of readings. It does work well doing it that way. I change my sensor every 6 days as well and when I said I let my battery run down I meant that I considered it run down after those 6 days. In my experience it would be dead in 7 days if I let it go that far (so in my opinion it’s close enough to the end to be considered run down in 6 days).

      • With my first one, I consistently always waited for it to die completely and get the lost sensor. I would then change sensor and charge transmitter at the same time.

        Typically, my old way left me with a bad first day because I didn’t insert the sensor the night before and a bad last day because the sensor was already running out of the chemicals on it.

        The way I do it now, I get reasonable accuracy for a much greater percentage of the time. Though, I still wouldn’t trust a closed loop system based on this technology.

  120. Jane says:

    Hi Scott and all,
    it’s been a real long time since I have posted here. (Feb 2008). I started with MM CGMS in Dec 2007, and also struggled until finding this site ! I used MM CGMS for over 3 years (same transmitter, never did die !). But last month I switched to Dexcom. I still use MM pump 522, and did not upgrade to the Revel.

    Anyway, Dexcom is a similar CGMS system, that many folks (including me) find to be easier to use, and more accurate then MM. Since switching to Dexcom, I see changes in BG trend (up and down) more quickly, and have learned how to better time my basals, bolus, meals, and exercise. As a result, my average BG has dropped 40 pts. If you want to find out more from others, check out TUdiabetes. There are lots of discussions and opinions on both, and much more than just CGMS.

    However, I rarely see anyone on TUdiabetes mention ISIG, yet I felt it was one of the most important learnings when using MM. When I switched to Dexcom, the Sales Rep(who is T1) had previously worked for MM. When she showed me the Dexcom, I said, where is the ISIG, or ‘equivalent’. She just laughed! However, with Dexcom, there is yet another device to carry around, since the Dexcom transmitter does not send signal to MM pump. But the sensor is approved for 7 days, and similar to MM, you can ‘restart’ it, and go for another 7 days or sometimes more.

    The ironic thing I have learned is that when you have achieved good control (less swings, more stable), both MM and Dexcom are quite accurate.


  121. All, I know this is only tangentially related to this topic. However, I’ve been having significant issues with my meter lately. Please check out a new thread about meter accuracy, or inaccuracy as the case may be.


    Is 20% close enough for you?

  122. Update: Please read my post regarding CVS Caremark. If you are in the U.S. and have any choice at all in your prescription drug coverage, you will want to avoid CVS Caremark like the plague.

    • nancy says:

      Still an issue for you? I had Caremark as my Rx supplier for 3 yrs. My pump and CGS supplies were all covered under the DME (durable medical equipment) benefit from my health insurance carrier, not under the pharmacy benefit. Also, I found they’d cover the Lily insulin with my doc’s Rx.

      • I only had them for a few months. I never got any issues with them resolved.

        Interestingly, I now have an Oxford HMO that pays for all diabetic supplies at the cost of a PCP office visit copay. It’s been working well for me not even having a drug plan.

        Of course, any non-diabetic medications I need are expensive as hell. But, they still come to less than the monthly cost of a drug plan. So, this may be an option for anyone who has Oxford as an option.

        I never thought I’d settle for an HMO instead of a POS or PPO. But, with not having a company paying any part of my health insurance now, I was lucky to be able to get access to this plan through a small business we own.

        Health insurance in this country is ridiculously expensive. I want the public option. I would buy into medicare in a heartbeat.

  123. Julia says:

    Scott, I stumbled across your blog while battling with getting sensor accuracy. I’ve gone through a number of sensors without getting meaningful data (ie sensor reading and meter reading is always out).

    There are times when my ISIG in under 10 and will not budge to rise. This is on the first and even second day of the life of the sensor. I’ve tried restarting the sensor, ignoring it etc but eventually dies because of calibration error.

    I find the accuracy during night time is mostly inaccurate. Most of the time it tells me I’m in a severe hypo state but i’m really not in hypo at all. Your mentioned calibrating only when you are not low or high, what range do you set that? Sometimes when I’m low (not that low), if the sensor and meter reading is very close, I calibrate, that was what the medtronic helpline told me to do.

    I seem to be wasting the sensors as I can’t get any accuracy out of them despite calibrating when stable.

    Also, can you give some suggestions on insertion sites? I usually do it on the abdomen but that doesn’t seem to give any accuracy any more so I switched to the buttock area but thats so difficult to put on.

    When I call the helpline about inaccuracy, they mentioned there is a number of factors and cannot pinpoint exactly which one I’m doing wrong. So the factors that are out of my control are injecting into scar tissue or the sensor dislodging from the site. But this can’t be happening every time!?!? I’m only getting about a 20% success rate with these sensors. So far i have 3 sensors that gave accurate readings, the rest are useless. I’m so frustrated.

    Hope you can offer some assistance.

    • I have not consistently had the types of problems you describe. I routinely hear, mostly from Minimed/Medtronic that abdomen is best. I don’t use it because I frequently wear backpacks with waste straps to take larger loads off my shoulders and move them to my hips.

      I’ve had pretty good luck with my buttocks. I find that going more toward the side, so you’re not really sitting on the sensor helps a lot.

      As for being a difficult place to get to, I find that doing a sort of a cross-over twist works. I hold the outside of my buttock with the hand on the same side, so left hand for left butt cheek. I always do this while seated.

      Then I use the opposing hand to work the inserter with my thumb on the button. One advantage of this is that the sensor is always always needle up, transmitter down, which I find more comfortable and less likely to have the weight of the transmitter pulling the sensor out.

      I then put a strip of 1″ wide 3M Gentle Paper tape over the sensor, across the top. And, after putting in the transmitter put a longer strip over both the sensor and transmitter.

      I sometimes find that it takes anywhere from 12 to 36 hours before the sensor begins giving truly reliable readings. This sounds terrible on something intended to only last 3 days. But, I get 6 days or even sometimes 7 out of each transmitter by simply lying to the pump/CGM after 3 days and saying it’s new again.

      Here’s a cheat for day 3, calibrate the sensor when it is nearly 3 days old, but not yet expired. Then, immediately after calibration, tell the pump/CGM that the sensor is new. It will keep right on working. As soon as it gets the next 5 minute signal, the graph will even pick up right where it left off. Note that this works with my Paradigm 523. With my older Paradigm 522, the steps were exactly reversed. I don’t yet know about newer models.

      So, what I generally do, assuming I remember on the last sensor day, which I sometimes don’t, is to insert the new sensor in the evening before the old expires. Then, in the morning, I take the transmitter off the old sensor, charge it fully, and put it on the new, telling the pump about the new sensor of course.

      Right now, you’ll probably want to cover the new sensor with either a very large bandaid or, if you’re cheap like me, a square of toilet paper folded into quarters with two strips of tape crossed over it. I usually only need to do this when my sensor bleeds a bit, for reasons described below.

      IMPORTANT: You will not be able to get the new sensor wet while it has no transmitter on it.

      I have a cheat for this that you can begin when your first transmitter dies. I use the dead transmitter as a cap for the new sensor while I have the old sensor still working in one butt cheek and the new one not yet working in the other. Unfortunately and fortunately, the transmitters are getting a lot better. You’ll probably have to wait 2.5 years or so before your transmitter dies and gives you this option.

      OK, all of that said, back to how to get better readings.


      My first question would be whether you are trying to use the sensor from the moment you put it in. I find that the ISIG varies wildly, usually too high, but sometimes stuck in the low range as well, until the sensor has been in my butt for 12-36 hours. This means that sometimes, even when I have waited 12 hours before starting to use the sensor, I do not get reliable readings from it on the first day.

      Most often on day one, what I see is a steadily declining ISIG value, assuming blood glucose remains relatively constant. This means the sensor would be telling me I’m low all the time.

      One thing I sometimes do, assuming the ISIG appears good, is to lie when calibrating. I add 5-10% to my BG value before calibrating. So, if my BG is 100, I might lie and calibrate to 105 on day one. Often this isn’t enough of a lie. Though, I still rarely have the guts to lie by much more than 5 or 10%. Perhaps I should try that on day one.

      Another thing that may help, since you’re trying your buttocks, is making sure you get up and move around somewhat frequently, especially when your sensor is incorrectly telling you you’re low. And, try massaging and kneading the area of the sensor. Grab a big hunk of your flesh around and including the sensor and shake or jiggle it. Almost anything you can think of that separates your skin/fat layer from the muscle underneath and moves it around will get the subcutaneous interstitial fluid flowing.

      Oh, you asked about calibrating when neither high nor low. I generally calibrate in the 80-120 range when possible. Though, sometimes I am forced to calibrate outside this range. If I believe that I’m high and the graph looks steady in a high range, I will sometimes calibrate when high. I don’t like to do this but do need to sometimes.

      When I do, I usually try to estimate how much my sensor is usually off by in the high range. I know that my sensor’s amplitude is less than my actual BG amplitude. So, when I’m 200, I usually see readings like 180-190. So, if I have to calibrate when I’m 200, I might give my sensor a reading of 185.

      IMPORTANT: After I calibrate in a bad range like this, I am much less trusting of actual numbers from my sensor. I generally trust the trend more than the actual values. Until I can give the pump/CGM a better calibration and later verify that the results are once again stable, I am very wary of the actual numbers.

      Nighttime values. Two things I can say about nighttime.

      1. Try not to sleep on the sensor. That always makes things worse.

      2. If you happen to be buying a new mattress, I can’t say it’s always the most comfortable, but the TempurPedic mattress I have generally puts less pressure on the sensor and allows it to work better if I do end up lying on it. I notice the sensor is sometimes much worse in motel beds, even when the mattress is good.

      Option 2 is an issue though. TempurPedic takes some getting used to and may not be the most comfortable mattress for everyone. I probably wouldn’t buy another. But, it is really better for this particular consideration. I do find I toss and turn less. But, keeping equal pressure on your whole body may leave you not perfectly flat, since heavier parts sink in more, which can be mildly uncomfortable at times. Also, without the pillowtop option which didn’t exist when we bought ours, it can be quite hard when the mattress is cold until your body warms it up.

      • Julia says:

        Thank you Scott.

        I’m a bit confused, the enlite sensors I’m using last for 6 days (supposedly) on a good run, not 3, are we talking about the same sensors?

        When I put the sensor on, i put the medtronic over tape on it before I put the transmitter on and then after I put the transmitter on, I put a piece of tergaderm dressing on top to cover it.

        Just in regards to the 80-120 mg range, thats a very small range. Maybe thats where I’m going wrong. I generally do 70- 176 mg. Very rarely can I get it within 80-120 when its time to calibrate.

        I do have a tempur and have been using it for a number of years now. So far I haven’t found I’m sleeping on the sensor so that isn’t too much of a problem. I’m still trying to find that sweet spot. I also find when I put it on the buttock, 100% of the time it bleeds a bit, is this a problem? I’ve read other trying the thigh area although not a suggested site by medtronic.

        You also mention that you cannot get the sensor wet without the transmitter. How long do you delay before putting the transmitter on to the sensor? Generally I leave it for 10 mins, the manual says 5 mins.

        Thank you.

      • Sorry. I use older Sof-sensors. I don’t know your sensors at all. Mine insert at an angle. There may be significant differences in the performance of our sensors, and possibly in comfort as well. I don’t like 90 degree angles on my infusion sets. I doubt I’d like them on my sensors. Both my silhouette infusion sets and my sof-sensors insert at around a 45 degree angle.

        That said, most of the advice regarding when to calibrate and leaving it in for at least 12 hours before attempting to use the sensor may be helpful.

        If you can’t calibrate at 80-120, it’s probably more important to calibrate when your BG is relatively flat. I find before a meal to be best. Rapidly rising or falling BG is a bad time to calibrate. The 15-20 minute lag makes it tough to time it right. I usually find that if my BG is moving, even slowly, waiting 5 minutes between doing the reading and giving it to the sensor is about right. But, it’s just a gut feel, not scientific.

        I put my sensor in the night before while the prior sensor is still working, and then put the transmitter on the new sensor the next day. So, I wait about 10-12 hours, when I remember and do it correctly, prior to putting the transmitter on the sensor. Even with that, I find that the sensor ISIGs sometimes drop throughout the day for a constant BG, meaning it may take anywhere from 0 – 24 hours to fully stabilize from the time I put the transmitter on. Or, that’s 12-36 hours since the sensor was inserted.

        One more thing you can try, now that I know Minimed/Medtronic makes 2 different sensors, is to try the other ones. Ask if you can try a box of the Sof-sensors. Unfortunately, everything I’m seeing indicates that I may have trouble getting my sensors going forward. That would be very annoying to me. They seem to believe that the new sensors, the enlite that you’re using, are more accurate. Unfortunately for me, I may find them very uncomfortable.

    • nancy says:

      Hi Julia – I inconsistently have the same issues you’ve reported, too. I say inconsistently because 4 out of 5 times, I have to pull the sensor out because of awful calc errors.

      Have you tried adjusting the angle? My CDE/pump trainer (also a long-term diabetic) advised against inserting at the 45 degree angle the original documentation recommended (also the angle the ‘feet’ (the part that sets on your skin) are set. (I use the Minimed soft sensors with a 523 Paradigm pump). The ‘sweet spot’ for me is somewhere between 90 and 45 degrees to the skin surface. Ideal is 60 – 65, but it’s all a WAG without a guide and with my variable inner tube around my waist.

      Scott’s recommendations about putting the sensor in and waiting several hours before hooking up the sensor and massaging the insertion site every so often (to increase the flow of interstatial fluid or break up the pooled blood from the capillary that ruptured during insertion – the latter is my thought, not his!) have been VERY VERY helpful for me and my results are increasingly better.

      The next ‘enhancement’ I’d like is sonar to know where the scar tissue and capillaries are so I can avoid them going in – that’s the #1 problem I have. VERY frustrating when it doesn’t work, but EQUALLY, VERY rewarding when it does!

      Thanks again Scott for starting this blog!

      Good Luck Julia

  124. Julia says:

    Thanks. For me the enlites don’t seem particularly accurate, its more a hit or miss. If ISIG drops to below 10, no matter how long i wait, the ISIG never goes back up. Very frustrating

  125. Perhaps you should see if you can still get the sof-sensors. I still have a couple of boxes. When they run low, I’m not sure whether I should try the new ones or whether I’ll have a choice in the matter.

    Have you tried massaging and kneading the area around the sensors? Also, try going for a walk and see if that changes anything. I know any kind of exercise completely changes both my ISIGs and my insulin absorption.

    I wonder if they’re either going too deep or not deep enough. They look fairly short, but going in at a right angle, they probably need to be. You might try areas of your body with more or less fat* to see if they work better in either situation.

    * Note: I’m not implying anything about your weight, just acknowledging that our body fat is not an even covering on our bodies, thankfully. Else, weight gain would make people look like Bibendum (the Michelin Man, yes he has a name).

    • Julia says:

      Thanks Scott, i think they phased out the soft sensors here. The only one available is the enlite. This is the only one that medtronic reps will teach patients.

      lol, its funny because I have been putting the sensor on my abdomen and its been quite in accurate. My buttock (which i think has more fat), seems to be giving my reliable readings so I’ve switched over there. So maybe the sensor works better in areas with more fat.

      I’m scared to massage the area, with the sensor being so sensitive to pressure, I’m scared I will dislodge it slightly.

      Can i confirm something with you. After you put on the sensor, 2 hours it will prompt you for a meter reading. Then the next calibration is 12 hours later (or at least thats what it says on the screen on the pump). But I recall something about entering it again in 6 hours for the first reading after the 2hr reading. Have I remembered correctly? If so, how important is the 6 hour reading?

      • I’m not sure just how outdated my current setup is. I have the paradigm 523 and am using sof-sensors.

        Yes. I need to input a reading 2 hours from the time I start my transmitter and sensor. There’s a bit of a but here. The but is that I sometimes hook up the transmitter and then wait until my blood sugar is stable to even bother to tell my pump that there is a new sensor. If and only if I do this, when I tell the pump about the new sensor, within 5 minutes, it will want a new reading. I tend to do this only when I put the transmitter on just before breakfast and know that it will be a while before my blood sugar stabilizes.

        As for the 6 hour reading, the technology I have definitely requires it. It is not at all optional. If I don’t provide that BG reading, I stop getting sensor readings. I also have the same situation when I tell the pump that I have a new sensor after 3 days, something you don’t need to do, but I do.

        So, with your newer technology, I can’t say how important that 6 hour reading is.

  126. steve says:

    I’m a bit confused by this talk of another kind of sensor other than the sof-sensor. I just checked and they are the only kind I can even see to order.

    • Strange. I just checked and can confirm what you say. Only sof sensors can be ordered at this time. However, when I was looking at the products section, only the enlites were listed. Now I can’t even find that page again. I suspect there is a change going on. I don’t know how gradual it will be for those of us who choose not to change.

  127. Jeff says:

    Haven’t read the whole reply thread (kinda long 🙂 ). New to CGM and only on third sensor. Having issues with the “WARM UP” cycle that seems to keep popping up… not just at the beginning, but just got out of the shower (had pump off) and kinda obviously got “weak signal” error, but it went into the 3-hour “silence” warm-up again. This seems to be a plague…

    Also seem to get calibration errors… notes say if you’re going to bed or similar, calibrate early; yet sometimes my “Sensor” menu doesn’t even show the “Calibrate” option, and when it finally does, here we go with the “warm up” cycle again.

    Hopefully I’m just confused and overlooking something obvious…

    On another note… sensors have left a pretty serious looking bruise twice… is this normal? Is there a trick to prevent it?


  128. Hi Jeff,

    That warm up thing should not happen. After weak signal, was the sensor lost? If so, try “find lost sensor” instead of “new sensor”. If not, I’ve had that happen a couple of times that I couldn’t explain. But, generally that should not happen.

    Calibration errors are a pain in the ass.

    I stated above and will save you reading the entire thread now, when you get a calibration error, whatever you do, DO NOT FOLLOW THE INSTRUCTIONS ON THE SCREEN TO METER BG NOW!!

    Doing so is guaranteed to get another error. Three strikes and you’re out. The sensor will be declared bad. After a calibration error, clear the METER BG NOW message and wait at least until the next, possibly two. Also check that your ISIG number is within range. If your reading is more than (I think 10) times the ISIG number, you will get a calibration error. Try massaging the site of the sensor to get fresh interstitial fluid there. That should help raise the ISIGs. Or, just get up and walk around. I usually have that problem when I’m just sitting around on my ass. (I use my butt cheeks for sensors and my thighs for infusion sites. I don’t do well with abs the way everyone else does.)

    As for the bruise, if the site bleeds more than a bit when you first put the sensor in, pull it out and get another. That said, I have been OK with sites that bled more than I would expect to work and they still did. I tape a square of TP folded in quarters over it until it stops bleeding. But, that’s when I get bruises.

    I think after a while you will probably learn what spots are less likely to bleed and bruise than others and stick to those. That sensor needle is annoyingly fat, compared with the infusion sets. Trial and error will help you find less painful and bloody spots. Sorry I can’t be more help than that.

    • Jeff says:

      Still getting a lot of “warm up” status when I try to view sensor data. I have had some “weak signal” cases (geezus, you drop your drawers to go to the can, and it registers a weak signal…) and it goes back into “warm up” state where you get no data for an hour or two followed by a demand for a new BG reading.

      I’ve tried to bear with it, but had a dangerous hypo the other day (EMS D-50 IV kinda serious) while it was “warming up”…

      • Have you resolved any of this issues? I’d love to hear what the problem was.

        BTW, regarding weak signal, the frequency of the transmitter is among those that are easily jammed by such things as microwave ovens, cordless phones, and cell phones. I wouldn’t be surprised if WiFi and bluetooth interfere as well, though I’m not sure.

        I keep my cell in a pocket on the opposite side of my body from my pump. I also always keep the pump on the same side of my body as the transmitter. They end up being a couple of inches from each other most of the time.

        Still, even with doing that, when I worked in an office, I would constantly get interference. Sometimes, it got so bad I’d have to go outside before I got the lost sensor message. I’m now retired and don’t have nearly as much trouble at home.

        Sorry I don’t have any more advice on this. I’d suggest working closely with the support team from Medtronic/Minimed. I don’t have high hopes for them resolving your issues, but don’t have any better ideas. Before Medtronic bought Minimed, most of the trainers were themselves diabetics using the equipment. I think that is no longer the case.

      • Jeff says:

        Thanks for the responses. My last sensor has been rather well behaved, and I’ve done the “double-up” trick going into day 6, where typically I would have (and sort of expected) issues about this time based on everything I’ve read about “stretching” the current sensors. They just released the new ones (forget the name) but they look promising… more accurate, and rated at 6 days out of the gate.

        But yes, I had a “LOT” of those periods of “warm-up”, sometimes on new sensor, sometimes on “weak signal”, sometimes if I didn’t enter a Meter BG on time, and sometimes it seemed to just do it to aggravate me. It would stay that way for an hour or more and eventually “find” itself again. I do a similar routine to you, I have the cell on one side and sensor/meter on the other, but perhaps I’m prone to other interference. I’m a network manager and we have lots of wireless access points at 2.4Ghz and 5Ghz everywhere I go. I thought however the sensors used a different frequency, given the plethora of interference on those bands.

        Speaking of which… it bugs the heck out of me that there is the “remote” thing that can be used to crank out a bolus “wirelessly”. I’m in network security… I’d rather that not exist 🙂

  129. Jeff,

    Minimed is using the 900MHz range for the transmitter. This is about the worst frequency they could have chosen. A friend is an engineer in wireless communications, e.g. writing software for mobile phone base stations and such, and assures me that this is the frequency most likely to be affected by other devices, especially microwave ovens and cordless phones and many other common devices. In any modern office full of cordless headsets, microwave ovens, and a zillion other devices, you will have problems. As a network manager, you will probably have even more trouble.

    You could consider playing with the setting for the warning time for the weak signal so that you have enough time to go for a walk and let the damn thing reconnect before you get a lost sensor message.

    We’re so inundated with various microwave transmitters at this point that I just have to wonder whether we’re slowly cooking our brains in addition to screwing up our CGM transmitters’ communications.

    On the other hand … what was I saying?

    I do try not to be too paranoid about the wonders of the modern world, like magnetic fields, microwaves, and all the chemicals and medications that end up in our water supply. But, sometimes it’s hard. The same electrical engineer friend who writes software for base stations resisted getting a cell phone for longer than anyone else I know. He still doesn’t usually carry it with him and won’t talk on it for very long.

    As for the wireless remote, I like it and would prefer that it also be able to receive messages from the pump/CGM and acknowledge them. When I ski, the pump is under layers of clothing to avoid having the insulin freeze. Then the alarm goes off. I have the remote in my pocket, but so what? I can’t find out what the alarm is or acknowledge it without peeling down quite a bit.

    What a pain!!

    But, I understand your concern about the remote. Just remember:

    1. It’s linked to the pump by serial number. *
    2. If you don’t enable the setting, it truly doesn’t exist.
    3. Unlike network servers, insulin pumps are rarely a hacker target.
    4. Insulin pumps don’t have IP addresses on the internet.

    * I have two remotes since I temporarily lost one. I have to have both serial numbers entered in the pump to be able to use either one.

    P.S. I’m a retired computer programmer. I’ve worked both in financial institutions and, briefly long ago, in defense. I also understand about security concerns.

    • The Expulsion Of Gods says:

      Hi Scott,
      Happy to see you’re still around, and, well, I just feel the need to ask if everything’s alright?
      Anyway, hope that it is.

      BTW, loved the discussion about birds and dinosaurs
      you others having.

      Sorry for being completely off topic, but I’m just concerned for your well being.

      • I’m still around. I was in Africa for 4 weeks to celebrate the start of my 6th decade on the planet. Thanks for the concern.

      • The Expulsion Of Gods says:

        The big sixty? And having that celebration in humanities place of birth? Wonderful!

        Carry on, carry on. And may you have many more to come.

        I’ll be around when you’re ready to continue.

        All the best

      • Thanks. Minor misunderstanding though. Beginning of my 6th decade means I’m 50.

      • The Expulsion Of Gods says:

        Sorry but, I like to agitate a little Mr. 50.

        I stand corrected.

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