Sensor Failure Indicators

Still learning how long a sensor is viable…What would be the main indicators that the sensor is failing?

Thanks for your help.

I can tell by the choppiness of the line. Here’s a sensor that’s performing well:

The transition from one data point to the next data point is relatively smooth. By contrast, here’s the line drawn by a sensor that’s at the end of it’s useful life:

Actual blood glucose movements in humans do not move in a jittery fashion. They are relatively smooth but in person with diabetes can elevate or dive relatively quickly.


A picture worth a thousand words! Thanks, @Terry4

With an older sensor (e.g. 2 weeks or more) sensor readings that are consistently >20% below fingerstick values are often an indicator that the sensor is on its way out. You may find that you need to recalibrate frequently.


The sensor is relatively stable and the reason for calibration and final failure is caused buy the healing process happing in the wound channel that’s created when it’s first inserted. Since the implantation of a sensor into the body is accompanied by growth of encapsulation tissue, then diffusion of oxygen to the reaction zone is continuously diminished. This decreasing oxygen availability causes the sensor reading to drift, requiring frequent re-calibration using finger-sticks and test strips. When your body heals to a certain point your sensor will no longer operate within it’s limits. The chemicals on the sensor are not degrade buy the oxygen sensing process and this process could go on for a very long time if the wound channel did not heal.

This one of the reason for such a big variation from user to user.

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Thank you for this excellent explanation, @JohnG! I love understanding the whys and whats :smile:

This is essentially what happened recently… a receiver reading of 105 and a glucometer reading of 206. Washed my hands and repeated with the same result. Did three more comparisons during the day between CGM and glucometer…none of the readings were as widely disparate, but all of them were > 20% difference. The day before, I did a long hike and spent a fair amount of time in the sun. Not sure how that could have impacted the sensor efficacy, but it’s the only change in my “normal” routine.

I changed the sensor, and am back to good results.

Your explanation makes a lot of sense. I’ve often wondered why some people on Facebook can regularly get 30+ days out of a sensor, while I have rarely gone past 15-16 days.

My current sensor is on day 24, which is the longest I’ve had a sensor last, but the past few days has not been giving me very smooth lines, although the actual readings (high, in range, or low) are still in the right ballpark. Since I pay for the sensors myself at $85 each, and I still test about 6-8x a day even with the CGM, I’m willing to put up with a fair bit before I change a sensor… Often I refuse to change it until it just stops giving me readings and goes to almost continuous ???s, which usually happens at just past the two week mark.

Incidentally, I read on Facebook that smushing the sensor around periodically can help disrupt the healing process and can prolong sensors. I don’t know if it works or not, but I often try it when I start getting weird behaviour, and it does seem to revive it sometimes and make it last a few more days. (This is, of course, not recommended by Dexcom, as they recommend against putting any pressure on the transmitter.)

Jen, where do you put the sensor? I have it on my thigh for the first time (previously on abdomen). It seems to me that the motion of pants up and down seem to be knocking into the dexcom . How do you, and everyone else address the practical aspects of the dexcom on the thighs? pants underwear touching the sensor, disturbing it…etc. I apologize in advance for asking such private, sensitive questions; don’t know where else to ask except this online community.

I’ve been using the Dexcom since the end of January and, so far, have only put sensors on my stomach. Since I pay for them myself, I’m nervous of putting one on my thigh and having it get knocked off. My thighs and arms in general do not like infusion sets (they get more irritated there than on my stomach), which just makes me more nervous.

One thing I do use is extra tape (Hypafix is the type I use). If edges start peeling up, I cut them off with scissors and eventaully put a bigger piece of tape over it. This helps keep the sensor secure. I’ve also seen on Facebook that people put self-adheisve wraps around their arms with sensors, which is something I would do if I was doing something active.

If you are on Facebook, the Dexcom community on there is amazing for finding solutiosn to Dexcom issus and for getting tips and tricks.