Earlier this week I replaced my first Dexcom G5 CGM sensor, after letting it run for over 16 days.
Here’s part of the graph shown by xDrip+ (the CGM that runs on an Android phone) for the old sensor. You can see the way the value is skipping up and down, and this is the “noise” in the signal. The line of translucent circles along the centre of the graph is xDrip’s activity indicator (it’s also keeping count of my steps) and isn’t directly indicating sensor noise.
At this point I had the new sensor inserted into my other arm and “pre-soaking” (with the tissue and sensor getting used to each other) before I moved the transmitter over to it. That way the values should be nice and steady when I transfer, without any initial noise.
Unfortunately I probably left it a bit late before starting the new sensor, as around 9pm xDrip started warning about excessive noise, and the values were jumping all over the place. My BG had actually climbed to well over 13 mmol/l but that wasn’t easy to notice from the graph. A closed-loop system is only as good as its data source, and the pump had in fact backed off as it thought my meal had been dealt with.
At 21:25 I started the new sensor (telling the system that I had inserted it earlier in the day and thus avoiding the 2-hour warm-up gap). However it took a few calibrations over the next hours to bring the new calibration into line as well as bring my BG down. Hopefully I’ll manage to do that much more smoothly on the next sensor.
It’s immediately obvious how clean the signal is from that fresh sensor! A day later the graph is still smooth:
Yes I was up at 3am for some reason (thus the activity indicator). But that peak in BG was from a late supper, and the loop dealt with it fine without much input from me. I had both the phone and linked watch still sitting beside the bed for a while (working from home that morning) which is why no activity showed until late.
Unless something unexpected happens, I’ll be repeating the process in another couple of weeks. Hopefully I’ll manage the changeover more smoothly though! I’ll be keeping a close eye on how jittery the CGM graph gets…