Dexcom forgets calibration?

I’ve occasionally been having this glitch with my G5: I get the calibration alert, do a finger stick and enter the info, see the reading adjust accordingly, all good… and then 10-15 minutes later the calibration alert is popping up and I have to do it again.

My hypothesis: it seems like this is a conflict between the iPhone app and the physical receiver. I carry both because I like to have redundancy: if one drops the Bluetooth connection the other usually remains connected. But it’s almost like the data I’m entering from one is getting countermanded by the other, or more specifically that the data I entered from the app is getting overwritten by the receiver, since I prefer using the app interface for calibrations. But I don’t know enough about the data flow between all these devices and the cloud to know if that’s true. I’ve always assumed the BG algorithm resides in the transmitter and it shouldn’t matter which device you use to update it: once the data has been registered in the transmitter it should be available to either device. But instead it’s acting like the receiver has some kind of priority, or maybe there’s a latency such that a bit somewhere in the network remains set to “calibrate,” and rather than picking up the bit that says “calibrated” it’s passing its own state back upstream and resetting the app back to “calibrate” instead.

But that’s all speculation–has anyone else experienced this and did you find an answer? Like maybe there’s a gotcha that says you need to do the calibration through the receiver if both are connected? Seems like a newish problem, like in the last couple of weeks, and I’ve been using both devices for a couple of years. Hoping to avoid an encounter with Dexcom tech support’s hold music…

Yes, I experience this, but I have a G4 system with just a receiver, so it is nothing to do with the APP. It seems to happen more often when the current Dexcom reading & the finger stick are far apart & even if the arrow is horizontal. I assume it is because it doesn’t like the reading entered & is saying “are you sure?”, usually the 2nd BG entered is fine.

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I agree with you.
I have G5, but don’t use Dexcom mobile just the receiver. It occasionally happens.

Interesting. I’ll have to see if that tracks. I think the two numbers were pretty far apart the time that caused me to post this. If it’s a deliberate feature it seems like a new thing. I only started running into it the last month or so. I did get a new set of transmitters somewhere in that time.

I don’t think it’s a new feature. I seem to remember it happening occasionally since I started with Dexcom over 2 years ago. I’m on Xmitter #3 & it’s happened with all of them. What’s annoying is that there is no audible alarm so I’m unaware the calibration has failed until I next look at the receiver. It keeps on showing readings all the time.

Interesting data points. I don’t know if it’s consistent enough to be a feature rather than a bug. I’ve definitely had this NOT happen when I’ve done an unscheduled calibration due to the G5 and finger stick readings being too divergent. I generally try to avoid those because they say it can cause greater inaccuracy if you do it too often, so they have to be pretty dramatically far off (> 20%). Maybe I’ll just have to break down and ask Dexcom. Their hold music isn’t that terrible.

I have always considered this to be a bug. I get this occasionally, even when my entered number is not very far off from Dex.

So you guys were right. According to Dexcom it’s been a feature all along–guess I just never noticed it until recently–and it does occur when the algorithm doesn’t believe the finger stick number and wants a retest. You’d kind of expect it to ask for a redo right away if the numbers are too far apart, but my meter log shows it was something like 30-40 minutes before I got the second alert. During that time the fingerstick number went from 132 down to 112 while the G5 stayed right around 100. Maybe it just needed sufficient time to see if there was any change under way before registering a second number.

Same thing has happened to me a couple times. In my case too, it seems there was a large difference in the numbers, even though the arrow was level.

I experienced this with the G4, but it seems like it only happens when the calibration is far enough away from the Dexcom result that it “appears” as an error to the algorithm - so it requests a new calibration a few minutes later.

It tends to happen to me when the calibrated amount is significantly high or low of the Dexcom level. As you say it is when the Dexcom does not believe the number. This might also happen when one is falling or rising rapidly.

Of course, it is a sort of a pain, but when I have that watermelon residue on my fingers I am reminded that it is good to have good tech.

I have had the same experience with the G4 + Animas Vibe. With the Vibe you have to wait until the bolus is completed and the pump
then asks you if you want to use the reading for a calibration (press OK). Sometimes it just doesn’t seem to register and 4 or 5 hours later I unexpectedly get an Enter Calibration message when I check my levels.


I use both Dex and Omnipod - like you i have both my iphone asking for data and the dex pdm - I find that calibrating using the Omnipod and inputting the value to either device works. The only time they “argue” is when inserting a new sensor - the pdm wins.