First Day on a Sensor

I’m on the first day of a new sensor and the thing continues to read very low. I calibrated around noon. A couple of hours later the below 55 alarm range and the thing read LOW and when I checked I was at 71. I think I’ve recalibrated twice since then when the spread has been >30%. But the dex is convinced it’s right and when I recalibrate it moves up so that it is just about 20% lower than the finger stick.

Do I -

  1. Just wait and pretend I don’t have a CGM today and give it a chance to settle in by bed time?
  2. Keep calibrating although the Dexcom doesn’t like so many calibrations?
  3. Restart the sensor and see if second time is the charm?

Thanks for any insight,


Maurie, this has happened to us before, and I don’t have a very satisfactory answer.

  • We have tried calibrating more than twice when that has happened, and it has given us OK results but not perfect in some situations, and in other situations we ended up wasting the sensor anyway (typically in those cases it was followed by a signal loss)

  • We have tried restarting the sensor. Once this sorted the sitation, but the other times it did not improve it.

This, along with early sensor loss or ???, seems to indicate a poor insertion and often creates, with us, a poor sensor experience for the (short) life of the sensor. Now when that happens I get ready to call Dexcom and get another sensor as soon as I get any more trouble. There is nothing worse than getting a sudden sensor loss later on when you are dropping precipitously and getting close to in-range - and, of course, that always happens soon after a problematic sensor that I keep it, thinking it will get better.

The weird thing about it is - when this has happened, it typically was when we felt the insertion had happened really well.

This is helpful. I wasn’t very happy with the insertion this morning. Nothing that I could put my finger on but…

Based on what you’ve described, that’s what I would do. Hydrate, and give it some more time to settle. I’d calibrate again only after bg comes up to a higher flat level. If Dex remains stuck, or if you get ???, it is probably time to replace the sensor, and call Dex for a replacement. In general, for better first-day experience, I recommend pre-soaking the sensor, as described by Dana Lewis.

I hadn’t called it a pre soak, but I do the same as Dana, and also saw better first day numbers.

This happened with my on my last sensor – After 12 hours of crazy numbers, mostly lows, I called Support, and they sent me a replacement – HOWEVER – around an hour or so later, it settled down! I did try the “3 calibrations 10 minutes apart” trick that’s supposed to reset the algorithm, but am not sure of that’s what helped or if it just started working. After that, it was FINE - one of the most on-target sensors I’ve had in a while.

I just removed it this evening after 21 days. There was some dried blood on it, so perhaps that was the problem? I’ll never know.

Wow they replaced that free but call an insurance company. Yeah.

Mine is still just producing crazy numbers although now they’re all way too high. I may try the 3 calibration trick and see whether it resets. But this raises a question that has bothered me for awhile. How does a closed loop system safely work when every so often a sensor/calibration is just bad.

Well, this does not exactly win your confidence! I would consider starting over with a new sensor and reporting it to Dexcom. I’ve often found that I get some blood when I pull it and the site is blood-fouled. Please report back what you discover. This doesn’t happen too often for me, like once or twice per year. Good luck.

I will report back in the morning. I was going to try Thas’s 3 calibration trick so I did the first calibration and then when I was about to enter the second number 10 minutes later the total difference was only 9 and I had a nice straight green line. Maybe it finally snapped to. I also drank a couple of glasses of water an hour or so ago so maybe I was a bit dehydrated. The problem with being our own science experiments is that we tend not to be very good at controlling for all variables :slight_smile:


Now you know why commercial closed loop systems are so limited (temporary suspension of basal). The Libre is one Sensor generation ahead. I am expecting that the 3rd gen plus algorithms will have the capability to verify its measurements independently for more accuracy.

After calibrating my sensor last night with ~120 versus the ~220 on Dexcom the readings turned normal within 15 minutes and were good all last night. All’s well that ends well, I guess.


Glad that’s working out - like I said, my last sensor had issues like that at the beginning. I was certain it would never recover, but get it a shot, anyway - and just removed it after 3 very reliable weeks.

FYI, the new one from the same box as the “complicated” sensor worked flawlessly from hour 2! Sure, it needed a slight settling-in period where it was a little off - but it has been within the +/-20% threshold from immediately after the initial calibrations. I think the dried blood on the old sensor was likely an indication as to what went wrong – but that one, and apparently yours, did get past that initial craziness. Glad to hear!

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