thank you for your responses, however, i am suprised to find out that more of you are not more upset with your cgm that gave you a reading that was over 100 points wrong. i may not be as liberal as you are, i was very upset if it wasn’t for my wife i could have had a serious problem with a reading that far off, were you told by the manufacturer that you could have a reading that far off ,mine said it could be 20%, but that is a lot more that 20% .

No doubt i am annoyed at a 100 point variance! But if it’s a one time in 6month occurrence, i let it slide. I have been tempted to rip my sensor off if it’s acting up really bad, but again, that’s a rare occasion. If i get the “???” reading on my receiver for more than 10 minutes or twice on that sensor i usually give up and pull it. Overall, it’s just a tool to help me manage myself. You are lucky you have a caring wife that will help you if needed, i’m pretty much out of luck if anything happens to me! a 20% variation is not great, but it’s liveable for me, the trend is more important than the numbers themselves. I do find that trend is almost always accurate even if the numbers are lagging or off.

I think this is a case of expectations. I do not expect my cgm to be the same as a finger stick. If I did, I certainly would be as frustrated as you. I also do not expect it to be off by 100. If it is, I try to go back and make sure it is not my own user error (entering bgs when my bg is not stable or is out of range, over entering data to try to “convince” the cgm that the bg is correct, etc.). Your original post indicated that you are new to cgm-ing. Perhaps joining the appropriate cgm group and gleaning the knowledge of others who also use the technology can help you get over this hump? Good luck!

A CGM should never just randomly be off by that large of a margin, there is likely a problem with it, either a bad sensor or a bad insertion site that is getting too much agitation or pressure placed on the sensor will cause it to go crazy. Sometimes overcallibration or calibrating on changing BG will cause the MM to go crazy, the Dexcom seems to handle callibrations better and have tighter accuracy. I have found that you still need to apply a bit of thought and common sense to the readings, if the reading seems off from what I would expect it to be I usually test to confirm the reading and usually my guess is correct. I the first day or two the trends are good, but I don’t put a lot of faith in the absolute value, once it has been giving me accuarate readings for a day or two I start trusting it a whole lot more. If you have a sensor that is performing poorly call the customer support line and they will replace it free of charge. They can be a bit erratic at times, but I am finding that certain sites work really well and others just don’t work and they seem to differ from person to person, I have gotten excellent results from upper abdomen and ok results from lower back, poor results from lower abdomen (belt seems to put pressure on the sensor when I sit down), poor results from butt cheek (i think that sitting down causes too much agitation), I am going to experiment with tricept and inner thigh in the near future.


Could you give us a bit of context for the reading that was off by 100 points?

  • Which CGM do you use?
  • sensor placement?
  • how many days were you using it before it gave the poor reading?
  • did the readings get better or worse in the following days?
  • what was the sensor reading and what was the fingerstick reading?