Issues with Minimed Sensor

I have the minimed cgms sensor and it has been frustrating me. It always seems to be a little behind.  It will say I'm at 90, but I test when I feel low and it's at 57. I treat the low and 20 minutes later it's beeping because I'm below 70. I went on a long bike ride, 4 hrs, this weekend and the sensor was off the entire time, it would say I was 207 when I was 143. It was incredibly confusing and I ended up testing 8 times in those four hours. I try to follow the calibration rules as best I can, but it just seems the thing is always off. Any suggestions? Anyone else have this problem? Is the dexcom any better?

Hey Abbey,

What you've described seems to be common with the Minimed CGM, from what I've heard others say.  I know that the MM gives you results every 20 minutes, whereas the Dexcom gives you results every 5 minutes - so there will be more lag time with the MM's results.  Either way, with any CGM there will be some variance (since it's testing interstitial fluid, not blood), and no CGM is ever going to be completely accurate, but the Dexcom seems to be the least sucky.  :)  I do use the Dexcom, so feel free to message me if you have any specific questions about it.


The MM system (and all other CGMS) are giving you results of interstitial fluid(I.F.), not actual BGs, and the I.F. can be 20 minutes behind what a BG reading is....and MM's info states exactly that.  If you're NOT getting good results use it as a trending device.  Find out what your readings are when it is reading numbers off target.  You can always change your settings in the CGMS, so it catch es your lows at a higher number than you have it set at now.  I have mine set for 70 for the low, and I know from years of experience with it that my BG is mostly at 55 at that point.  Since in hypo-unaware, and can function quite well at 55, that 70 setting works for me.

As for your bike ride results....sounds like you were coming down fast from exercise.  Did you lower your basals 2 hours before exercise so that such a dramatic low did not happen (I'm going to assume you're a pumper too).  You can't expect it to be spot on during exercise since most people when they exercise have a drop in BG. 

If your sensor is never spot on (mine rarely is!), then it sounds like a calibration issue.  I know for myself...if i can get a good calibration, I can usually get results within 10 points of my BG readings AS LONG AS I'M NOT AT THE EXTREME ENDS (low or high).  The sensor does take time to catch up with the actual BG.

Do you use the Carelink upload option and take a look at the graphs available?  The can be VERY helpful in looking for trends, thus letting you more easily adjust basal settings.

Don't expect it to be 'spot-on'....unless you BG is very stable(like for more than 20 minutes).  The MM sensor gives you a new reading EVERY 5 minutes (not 20 as a previous poster stated).

Keep in mind it's not a perfect science, but if you use it long enough, it gets easier.  If you've just started....then there is a STEEP learning curve!

Hope that helps (HTH).  Michelle  MM722 (4 yrs) and MM CGMS (2 yrs)

I also have the minimed sensor, which updates every 5 minutes. I get lots of problems all the time with it not calibrating properly. I insert it correctly (usually, sometimes it starts bleeding like crazy and then I have to keep retrying) but then it does not work for any apparent reason and I keep saying 'new sensor' but usually it ends up with 'bad sensor.' I stopped using it altogether for a few months because it was bugging me so much. Lately, I've been having a little better luck. I test my blood sugar every 2 hours and I think that will keep it closer to the meter reading; at first I tested every 12 hours because I thought the point of it was to not get tested as much, but I think if you let it go longer periods of time then it will become increasingly inaccurate. The minimed rep told me to always be very well hydrated for it to work at it's maximum potential, so if you were on a bike ride and getting sweaty that may have something to do with it. I also have the lag time problem, I'm low and it doesn't say I am yet, etc. but it says it has a 20% variance. When its way off like that I just have to hope that it will recalibrate itself properly, sometimes it does and sometimes it doesn't. I think since the sensors are fairly new technology, they will keep coming out with better ones that are more accurate. I'm just glad I am not the only one who is frustrated too.

yay! I'm glad to have someone with me in the trenches.  I guess calibration is the golden key. I agree with you Kelly, that the new version will be better. 

Kelly, does it help to calibrate it that often? When I started the sensor the minimed rep told me not to update it too often, so i try to do it at the 12 hour mark, but it lags or it'll just be way off. I've had so many problems with it that I rarely wear it anymore. It's more frustration than it's worth. Do you think more calibrations would help?

I used to do it every 12 hours and it would be completely way off, so I stopped using it for almost a year in sheer frustration. A lot of times it wouldn't insert correctly either, either with bleeding or not going in all the way. I decided to try it again and every 2 hours is keeping it a lot more accurate. You just have to be careful around the times you are exercising or eating because the sensor might have trouble adjusting itself to rapidly changing blood sugar levels. I would try more often than twice a day and see if that helps a little. I am glad I am not the only one out there who is finding these sensors don't always work as well as they are supposed to!

I have been told by MM, trainer and other list users to calibrate the MM at most 4x/day.  I have had much luck with doing it at least 3x/day for most days, trying to do it only when it is stable and will be stable for at least 15 minutes afterward.  The only time I would calibrate more than 4x/day is if I was restarting a sensor for it's 2nd round of use and the restart was mid day.  Most of my restarts are bedtime or morning, so that doesn't happen too often.  On the RARE occasion if it is not tracking well, I might try to calibrate it 5-6x/day.  It all depends on what my actual BG is and what the sensor BG is...and how far apart they are.  I don't want to calibrate it and get a calibration error!

I usually wear my sensors 9-12 days...........and have been pretty lucky in getting it to restart the 3rd time after recharging the transmitter and reconnecting.                      

Hope that helps!

Michelle, MM722 and MM CGMS

Hi Abbey,

I've been reading your blog.  Congrats on finishing the Iowa bike ride!  I also have a Mini-Med sensor, and I find that it lags.  Remember that it gives a blood sugar about every 5 minutes.  Someone else commented on only calibrating 3-4 times a day, which I find works.  Also, don't calibrate when you are high or low or eating or exercising (when does that leave??).  Remember that your meter is your best bet.  I find that the sensor eventually comes in line with my actual blood sugar level.  When I was having problems, about a year ago, my doctor told me that the transmitter only lasts about 2 years with light use, and shorter with heavier use.  Maybe your problems are from an aging transmitter.  Good luck, and keep on blogging!

Thanks for the advice! Calibrating only 3-4 times a day has really helped! and now since my blood sugars are more stable and not bouncing all over the place, that helps too. I didn't know the transmitter only lasts two years though! ugh.

Thanks for reading my blog:)

No guarantee that transmitter will last 2 years.  Some do, some don't.  MM only guarantees if for 6 mojmntjhs if I'm not mistaken.  I think I've seen one person on another list I belong to say hers is now 28 months old....I only hope mine lasts that long. I wear mine every day!

Hi Michelle

I have read your replies to the questions and you seem to know a lot about CGM's, I am going for my training tomorrow and wondering if you have any suggestion about the best site for the CGM to be inserted?



Hi Carlos.  I've only used my stomach or front of thighs, but have had very few failures.  I live alone, so it is almost impossible for me to insert in my arms, but I know of others that do it there and have said they have great results.  Not quite sure how you'd insert in arm area and then be able to connect the transmitter!  Just my opinion, but others have said it can be done!

If I use my thighs, I use the front of them.  On the inside I find it tends to come detached as my inner thighs rub together.  I also tend to use the higher up portion of my thigh.  The 2 times I used nearer to my knees, I had terrible times getting it stay stable, and had the worse rash I've ever seen since using the MM CGMS.  Some people use the outer thigh and have great luck.  It sort of depends on where you have the most body "real estate" to use!   I would guess that more than 75% of my insertions have been on my thighs.  I do occasionally use my stomach if both my thighs do not look good, or if I've had a problem and had to remove before the 5 days cycle is complete.

The most important thing I can suggest is to insert the sensor at a slightly deeper angle than what the inserter is intended for.  A lot of other users I have talked to say the same...Make sure the angle is deep enough to get good staying power. 

The other important thing is to tape it down SECURELY!  You don't want it to move when you are moving.  Taping securely can help minimize the movement and make the sensors last longer!  Call MM and request they send you the taping kit and tips (free).  It comes with several types of clean over tapes (Tegaderm, IV3000, Tegaderm HP,  and several other 'sticky' options.  Give them all a try and see what works best for you!

Don;'t forget that after the initial 3 days, you can go in to your sensor menu and pick "start new sensor" and get another 3 days of usage.  Many start it a 3rd time and get an extra day as the connection between sensor and transmitter must be broken at day 7.  Be careful if you untape the transmitter at day 6 or 7.  Most people recharge the transmitter at that point, although it is not mandatory.  I do recharge as I want to 'try' and get as much time out of a single sensor as possible.  When you take tape off at day 6 or 7, hold the sensor in place with  your fingers as you don't want it to move/pull out.  Might take a few attempts on a the 1st few sensors you use to get the hang of it.  It gets easier the more you try!

I'm on day 8 of my current sensor.  Inserted it Last Tuesday around supper time.  Waited the 2 hrs for it to get 'wet' and then turned it on.  Fairly quickly it will ask to be calibrated.  You need to do 2 calibrations within the 1st 6 hrs, then it needs a calibration every 12 hours.  Calibrate when your sugars are fairly stable (not before or after exercise or eating).  I find I can calibrate when I get up (530am) and then usually calibrate before lunch, usually at 100pm.  I like to try and calibrate every 6 hrs so I'm not caught off guard when it DEMANDS a calibration!  MM suggests to not calibrate more than 4x/ only confuses the sensor!  Don't calibrate when you seeing double up or down arrows!  If possible, try to calibrate when our sensor readings are off by only 2-30 units than your actual BG....if there is too larger a difference in the sensor BG and that calibration might get a calibration error.  2 calibration errors in a short period of time will make the unit think it's a bad sensor.   Don't disconnect...just turn the sensor off for 15 minutes or so (or until your BG's are more stable) and try "start new sensor" again.  We have found that sometimes we can fool the device into    napping and then getting it to work correctly!

I have found that my sensors start the best if i hook them up before I go to bed and don't turn the sensor on until morning.  it allows the sensor to get 'wet' enough and work better.  Many others have found this works well too!  Sure,  it means a night without readings, but it does give good results when it is started!!!

I have a whole list of tips saved in a file in my documents...just holler if you'd like to see them.  They have been gathered from other users more wiser than me...and are very informative!

Hope that helps!  Don't be discouraged.  The 1st few weeks are the toughest to get things down to a ritual.  There is a steep learning curve for most who use the CGMS, no matter what type you use!


I had the Minimed sensor for about a year and wasted a lot of sensors due to not being able to get it inserted correctly.  I recently switched to the Dexcom and it is soooo much easier.  I am trying to get pregnant and wanted to have something reliable to assist me in that journey.  I have found it much easier to insert and much easier to keep going.  It lasts 4 days longer than Minimed and you can calibrate it as much as you want without compromising it.  The minimed does not suggest calibrating more than 3-4 times a day.  Who knows why?  Anyway if you have good insurance it will pay for the entire thing and the cost of the sensors are considerably less.

Thank you Thank you Thank you Michelle, you gave me so much information! I had the training session yesterday and since I had read your comments before i had the training I was then more prepared!! it wasn't that bad and I am loving the information it gives you, I think I am becoming a bit paranoid about the targets and want to keep the trend line within those limits!! I am looking at the thing almost every 10 minutes ha ha

I had a low on the night so the alarm was going off so often! but managed to get it under control and had a good night sleep after that.

I would love if you can email me the tips that you have, my email is

Thank you so much!!! :)