Are Some Sensors Just Not as Good?

I started my Dexcom a couple months ago. My first two sensors were wonderful - after the first day, they perfectly matched my blood sugars (within 5 points) almost all the time for 20+ days. However, on Monday, I put in a third sensor. For a couple of hours, it gave me readings that were about 30 or 40 points from my meter before it gave me the ???. After 12 hours or so, the ???s finally stopped, but it still isn’t as accurate as my previous sensors - it’s almost always at least 20 points off and frequently 50 or more. I keep hoping that, if I just give it more time, it will become more accurate, but it isn’t.

I don’t know if I’m spoiled because my previous two sensors were so great or if I should request a replacement for this one. So do most sensors usually have you 20 to 80 points off? Am I expecting too much from my Dex? Or is this kind of a bad sensor?

Thanks, my experts!

could be a couple things as ive learned the longer the sensor is in the more accurate it tends to be, it could also be a bad sensor, i also think it tends to go off where you put the sensor sometimes as well…

I have been in ??? hell many times. Once I actually called in to their tech support and they told me it can also be caused by a lot of fluctuations in your levels. If I go low and then spike super high it seems to cause issues. I also think that I have had a box of 4 where this occurred more frequently so I would say there are definitely times when you just get duds. Good luck!


Last week, for a couple of days, I was so frustrated with my readings being so off.

The last two days, (day 11 and 12), the same sensor has been so amazingly accurate.

So, I would say, there are a lot of factors that may result in bad readings. The same sensor could later learn to be very accurate.

I am glad that you got off to a good start and have seen sensor nirvana. I just pulled a sensor after 3 days that was as bad as your sensor. There are definitely good sensors and bad sensors. I have not figured out how to make sensors tick accurately all the time. Some sites seem to be better than others. I have not found a site that delivers good results all the time. We are early adopters. Accuracy will get better with future generation sensors. Hang in there and make the best out of it.

One thing you can try if you haven’t changed the sensor yet. Carefully remove the transmitter from the sensor. Clean the transmitter contacts with an alcohol pad. Carefully clean the sensor pads with an alcohol pad. Put the transmitter back on the sensor. Stop the sensor, start the sensor. Make sure to calibrate the first time when your blood sugar is stable.

That might fix it.

Also remember these things are put together by hand, or so I am told. If you have ever torn one apart after it has died, there are a lot of itty-bitty parts to put together, so it could be possible that you got one that was made on a Monday, a Friday, or at the end of the shift! (Lol!)
Aside from the human aspect of making these, there is placement, how hydrated you are, exercise, did it bleed upon insertion, etc that can contribute to off readings. My current one began good also, and now today has read higher than normal a good part of the day even with calibrations. It’s probably more “me” than the sensor, but it sure is sweet when the numbers align oh so perfectly!

Yes, there ARE Sensors which don’t perform as well. Sometimes it’s an invisible issue with the Site. (Subcutaneous Tissue is not 100% consistent.) And sometimes, it’s the actual Sensor. I would not go for more than 24 hours without good readings: download the data, so that you can send it to Dexcom support for Credit, then replace the Sensor. Do be 100% sure to always wipe your Transmitter clean before insertion; IPA pads are good for this. But I use 90% IPA from the bottle with a Q-tip: I wash it clean with one end “wet”, then further wipe it with the other end “dry” to make it absolutely spotless.

20 mg/dL is pretty bad. And, IMO, 50+ is absolutely unacceptable, dangerously misleading.

Thanks for all the advice, guys! As soon as I figure out how to download the data into my computer, I’ll call and ask for a new one - whether it’s my fault or not, I have to have an accurate Dex.