Dexcom G6, new sensor, how many calibrations should I try before I give up?!

I installed my first G6 sensor 2 days ago, I was fasting and xDrip in native mode showed a reading 30 mg/dl higher than my fingersticks. I waited a couple of hours after warmup and tried again, it was still high so I calibrated it with a fingerstick reading, within an hour it was still 20-30 pts too high. A few hours after I broke my fast last night and again this morning I did some more fingersticks and found it was high by as much as 55 points. I have added 3 more calibrations over the past 5 hours when my glucose was stable and it seems to be getting more accurate.

Should I keep doing calibrations in the hope it will finally give accurate readings, or should I give up on this sensor and put in a new one?

What BG reading is your meter giving you? What meter are you using? The G6 uses the 30/30 rule, anything within 30 percent is considered accurate.

I’m using a Contour Next, here are the 2 worst examples:

last night the Contour showed 80 mg/dl, G6 was 121.
this morning Contour 109, G6 152.

I used a Libre before but I switched to the G6 because it is supposed to be more accurate, I’m hoping this is a bad sensor otherwise I’m not impressed!

Definitely a wonky sensor. I’d replace it and have Dexcom send you another one

I almost gave up on one that was really off, I kept calibrating it and it started asking for confirmation calibrations too. Somewhere between 24-48 hours it started to behave and has been restarted and behaving still. But I kept repeatedly calibrating as I figured if I froze it I had nothing to lose as I would just be calling it in otherwise.

I rarely calibrate my G6. My personal approach is an assumption that for the first 24-36 hours after warmup, the sensor is getting acclimated so I wait it out. If after 36-48 hours it hasn’t righted itself, its most likely never going to.


For me my G6 always goes up and down much faster than my BG can be in the first few hours (up to 24 maybe). Calibrating in this time period just throws the later days readings off:

Well, that’s consistent :wink: 41 high then 43 high. I don’t know how the transmitter handles the calibrations, most likely no one outside Dexcom does (as the ‘uncalibrated’ readings aren’t available.) xDrip+ seemed to use a straight line on the G5 and earlier. A straight line fit to two points with random errors will throw the readings outside the two points way off. Whatever algorithm Dexcom is using internally it can’t fix random errors due to a sensor which is still stabilizing.

I suspect that once calibration has been started it is always better to continue it, so long as our actual blood glucose is stable. Stable means no significant variation over the last 30 minutes (6 readings) because the fingerstick is approaching 5 minutes (1 reading) in advance of the G6.

Ah, well. It’s all spin; the G6 doesn’t say anything for the first two hours, then it spurts random numbers for a few hours, then it runs to 240 hours being fairly accurate. So if you average the errors over time then you get a much lower error than you get over the first day, unless you assume the first two hours errors are infinite :wink:

One of the things my G6 does is to suffer drop outs every now and then, maybe once or twice a day. During these dropouts the readings suddenly start descending towards 0, then this stops and they jump back to something like the pre-descent reading. So the transmitter is seeing bad news and, I suspect, guesstimating the right answer. This is somewhat curious.

The obvious answer is to have two G6 sensors running 5 days apart and swapping between them as appropriate. The obvious (no patents please) way to do that is to have the transmitter connect to two sensors either of which can be swapped out as needed.

Thanks for the input, everybody.
I kept at it and after 3 days it got remarkably accurate. A couple of times in the past few days since then I looked at an xDrip reading and thought that it was off but when I checked with a fingerstick is is usually with 1 or 2 points.
I’m back on team “yay G6!”
I think on the next sensor I will wait it out without calibrations and see how that goes. At the very least my fingertips will thank me!

1 Like