Quitting the CGMS

Hi there all,

My Minimed CGMS is never accurate. I have tried everything: sensor placement/ replacing transmitters and sensors/tapes/ a strict schedule around calibration etc. etc - for almost a year. Occasionally I’ll get a run, but usually only 1 day out of 10 or so.
I’m wondering if my body chemistry just doesn’t like it. Or if my low carb diet gives me interstitial chemistry that the sensor doesn’t like.

Either way I’m simply sick of the alarms shouting that I am 40 when I am 150. It’s causing me more stress that it’s worth, I think.

Anyone else give up due to accuracy issues?


I gave up my MM CGMS after about 3 weeks of use. I’m now waiting on my Dexcom next…I’m hopeful that it’ll be more accurate and useful to me.

When i first started i was very frustrated. It either wasn’t working right or i didn’t know what i was doing. I gave up on it for about 10 months. Then i started using again at the request of my girlfriend. I started to get the hang of it and liked it. That’s when i went to a concert and lost it. I just had another shipped out to me about 2 weeks ago and i’m trying to start again. I think i just need to get used to it, but it sounds like you’ve given it a fair shot.

Quitting CGMs or quitting MM CGM? I am a dex user for 6 weeks and love it. Cannot image life without it anymore. Try the other 2 brands. Maybe they will work better for you. When my bg meter and my dex don’t agree by a wide margin I test with another strip. Amazingly most of the time the 2nd finger prick comes in close to the dex. I never knew that the bg meter readings varied this much until the dex calibration procedure made me take 2 tests in a row.

I suppose I mean quit the MM- enough people are saying that they get better accuracy with the dex that I might try and see if my insurance will cover it.

Ruth, I am glad to hear that you are not giving up on CGMs. My dex is very accurate. It has happened that I felt low, the dex showed 100 while the test strip came back at 60. However, 10 minutes later the dex showed 60. It took me a while to figure in the delay and predict based on the up and down arrows where my bg is now. If the down arrow indicates a fall of 2 mg/dl I mentally adjust the dex reading down by 20. I have the feeling that a lot of the reported inaccuracies stem for comparing bg level that are 10 minutes apart (dex showing 10 minutes ago, test strip showing now). Another way I try to deal with this delay is by making my bg move slower.

Hi Ruth! I am new to this site but I have been asking your same questions myself. I have been a diabetic type 1 for 25 years now and on top of tat I am categorized under the Brittle Diabetic person. I have not have a good look with MM CGM and I questioned my body chemistry too. By what the MM CGM help line people had come to conclusion with me is that since my Bgs change so quickly and I have to test so often to verify if I am really going low or hi so quickly by me testing the bg the cgm mechanisim takes it as if I am calibrating too soon or too often so maybe the system is not meant to deal with brittleness like in my case. That shocked me because I thought this would be the answer to our prayers due to te rapid changes in BG values from 1/2 hr to an h/r any time, any giving day. Ruth also you mentioned body chemistry and I have a question for all of you on this website: Has anybody have problems with Bg results been inaccurate one after the other even by using 2 different glucometers, different lots of test strips, new batteries on each meter, which had been tested with control solution for accuracy at that time and drawing blood from the same finger for 2 sets of bg tests for the different glucometers? In my case sometimes the bg results go all over the place from 245 to 56 to 196 to 74 to 184 to 274 etc… and right after the other and those are test done at the same time from the same finger in sets of 2 test strips for 2 different glucometers. The problem does not happens to me every single day and when it happens I keep testing my bg with both glucometers; last time it started at breakfast by lunch both glucomerters where reading my bgs within range of each other and not all over the place and in tune within normal readings. Just a curious question from a very hard to control brittle diabetic. Though I have to emphasize my A1HC is 6.3 and I test 10 times every day within normal conditions and more when I am too all over the place BG wise. Hope somebody has some answers for us!
Take care,

This has happened to me when I did not wash my fingers before testing.

Thanks for your reply but I had wash my hands already before the low bgs and we took bgs from clean fingers a total of 16 times. This does not happen to me every day but when it happens; it is just so hard to understand. My endocrinologist gave me a lab order for when this happens again to go immediately to the lab and have some tests done. just in case there are some changes that would give him a hint of what might be happening to my body during those episodes… Have a good day Helmut and thanks again!!!

I keep trying with the MM CGMS, but keep getting frustrated. Like yourself, it will be on for a day or two and then way off. The problem really is all the alarms the thing has. If it’s amazingly inaccurate and only is useful for the trends, then why bother with all the alarms? It wakes me up every night I use it for no good reason, so I have initially gone to shutting it off at night. However, it regularly starts alarming in the middle of my work at which point I am not able to shut it off and then it will just go on vibrating for the next few hours bothering me senseless… So now I’ve gone to shutting it off while at work as well… What’s the point?

I wish they would let me sign some sort of consent and shut off the alarms… That would at least allow me to get some sleep and not be disturbed at work.

I was having inaccurate results from my MM CGMS and called Medtronic support for help and found out the following information:

Sensor is a semi-permeable membrane best to place in abdomen
2 hour start period is for saturation of membrane
Glucose from your body reacts with the membrane to send a tiny electrical current from your body that helps to calculate glucose
The current is measured in ISIGs (Input Signal)
The ISIG is then equated to a BG reading from your meter (eg. sensor sends a reading of 13.1 and your meter BG reads 102 so every time the sensor sees a 13.1 current reading it reports to your pump that your BG is 102)
Checks every 5 minutes for a total of 288 times a day
Meter BG should be manually input instead of letting meter auto-update
Have to put in meter BG 4 times a day (before breakfast, 4 hours after breakfast before lunch, 4 hours after lunch before dinner, 4 hours after dinner before bed)
Meter BG can be +/- 20% different from Sensor BG

Now my problem was that I was using the CGMS as a replacement and not a supplement and trusting that the CGMS could calibrate itself. I was also using the number that the CGMS was reporting to update itself which would drive my numbers down. I should have been checking my BG 4 times a day to calibrate my CGMS which I am now doing and seeing more accurate results. Hopefully this information will help others. I never attended a training class and learned how to use the CGMS incorrectly all by myself :stuck_out_tongue:

My wife has the Minimed CGM and it used to never be accurate either. Well after reading these forums we learned when to calibrate and when not to calibrate. The accuracy has improved significantly. However the sensor seems to generally be a lagging indicator.

So here is when she calibrates. She only calibrates when her BG levels shows a flat trend (so not going higher or lower; no arrows). She only calibrates when she is between 80 and 140 (or 120 I am not sure off the top of my head). She only calibrates when the ISIG is above 8.

Based on experience and recommendation you should never calibrate unless the ISIG is greater than your BG meter check divided by 20. Example: Let’s say your meter reads 140. 140/20=7. So the ISIG needs to be greater than 7 for an acceptable calibration. Otherwise you might get a CAL Error.

I have had the Minimed CGMS for almost a year now and I have only once had readings that didn’t correspond within 20 or 30 to my finger sticks. I guess maybe it doesn’t work for everyone but if you calibrate correctly it can do wonders for you. I used to have lows all the time that I could not catch and would end up unconscioues, I still get the lowas occasionally but the alarm notifies me before it gets too low. I have heard both bad and good stories about the dex as well. It just takes a little patience to get used to them but they are well worth it for many people.

Ruth, I gave up on the MM CGMS because of accuracy issues (and comfort issues as well) last year. I wish I knew why but I think for some people it just isn’t accurate. I use the Dexcom now and am very happy with it. There are instances when this one is off too but it’s not often at all. You don’t have to worry about when to calibrate the Dexcom like with the MM and you only have to do it twice a day instead of 4 times. It’s a separate receiver but it doesn’t have to be left “on” you like a pump. If your insurace won’t cover another CGMS, I actually turned my MM transmitter to Dexcom toward the cost. Maybe you could look into that. Good luck!

Sorry you had such a hassle. Maybe I’m a lucky one then, as my MM722+CGMS is pretty darn accurate. I am hypounaware so I really was interested in the “tren” feature, but everything has worked good for me.

I made the switch from DexCom to MiniMed two months ago at the same time as trying out a pump, and have found the MiniMed to be materially less accurate.

Make no mistake, the DexCom would sometimes get way off in its readings too, but the MiniMed unit seems particularly susceptible to not catching lows - I have had numerous hypo episodes, including several VERY SEVERE hypo episodes (glucose at under 40), where the MiniMed CGMS showed me to flat at 100-130+, such that even the glucose trend over a period of hours was NOT being accurately read/depicted.

And the funny thing is, they say you’re not supposed to use it to treat, always test yourself before you do anything and then it can’t hurt, but I disagree vehemently with this idea. IMHO, if the system is giving you false information about your level and/or the direction of your blood sugar, it’s better to be aware that you don’t know your level than to be told info of questionable value, because you will always attribute some level truth to it, and that can be dangerous.

I’ve also had a lot of problems with the system reporting bad sensors, etc., and have already had the transmitter replaced once and half a box of sensors replaced in an effort to find the problem. If we don’t have it figured out in a couple of months, I’ll be trying the Freestyle Navigator system.

As I read these posts, I feel “luckier” each day. I just tested and my finger stick=97. My MM722/CGMS=97. I just can’t get more “right on” than that. Happens very often for me too.


I am on the MM and have had the same problems. But I have found these issues.

1 The damned thing is about as useless as breasts on a boar hog on the first day.

2 NEVER trust the numbers, I know, the idea is to be able to tell where you are and if you really look at it for what it is, a gauge to where you are, then it works. I too am upset when it says that my BS is 130 and I am really at 60, that is too far off but usually if you test and record when you first wake up and then can manage to go without eating for three hours, it is accurate enought to be a decent gauge.

I had an episode the other night, where my BS went through the roof and had a hell of a time getting it down. After about six hours and 40 + units of Humalog it finally came down. The good thing is that the sensor was pretty much on the money.

  1. Don’t believe the MM techs. If it is working good you can leave it in for six days. The only time I change out the sensor is when it is totally messed up for all three days and if I get a good one, I just reinstate it for another round instead of changing it out. It has nothing to do with being a cheapskate since my insurance covers these at 100%, it is a matter of accuracy and I think that the last three days that I have it on are the most accurate days.

Also consider the Navigator. Mine is fabulously accurate and has all the CDEs and docs at my office suggesting it to more and more people. My CDE said she started 8 new patients on it recently.

I wore the MM for three days and the Dex for 7 (both borrowed from my endo’s office) before deciding to order the Nav. I have zero regrets. Their customer service has been great, too. The device is as comfortable to wear as Dex, and both are inifinitely more comfortable than the MM “spear.”

Funny - I haven’t really compared the under the skin portion of the sensor, but I HAVE noticed a lot more discomfort with the MM sensors, and actually wondered why, as the wire didn’t seem that much bigger to me from memory. So when you compared them, the difference was substantial?