I wrote in my last post about a Dexcom G7 sensor which for me was only supplying data 97% of the time. That meant that it missed checkins and combined across the entire day it didn’t respond for just over an hour. Mind you, that metric doesn’t capture how long it was offline for each time: when it reconnects it fills the missing data even though the automated insulin delivery (AID) system wasn’t able to act on the data in real time (and with insulin the timing of the doses can make a big difference).
This article is just a follow-up to that now the sensor has aged slightly. I’m still using that sensor, and now on the 7th day I can see it’s currently only getting an 85% realtime capture rate.
This means that for more than 3.5 hours out of the last 24 there’s been silence. The last gap I saw was 20 minutes long.
Even back in the days of G5 I observed that getting below 95% could negatively impact the final TIR/etc. 85% is just ridiculous.
Sensor comparisons
I’m not currently using that G7 to drive my AID system. I’m not prepared to take that risk, and I’ve just left it in to observe.
I’m currently running off a G6 which is on its 3rd day. And just for laughs I also have another G6 which is at 24 days! Anubis transmitters don’t kill off the session at 10 days but are otherwise the same as a standard G6 transmitter. I was using this sensor weeks ago, but left it in as a cross-check (especially as initially I only had it and the G7 – in between I used a standard G6 transmitter on another sensor).
So let’s see what last night’s data looks like…
The G7 sensor is achieving a real-time capture rate of only 85%. The youngest G6 is at 99%. The old G6 is at 98% (although the difference between 98-100% is miniscule).
Sensor readings can occasionally jump a bit. Sometimes due to just physical impedance (“compression lows” are an extreme example). You can see that even the young G6 occasionally jumps a bit. And the very old G6 is well past its prime, jumping up/down occasionally before continuing.
But the 7-day-old G7 is still jumping all over the place. And not consistently providing data. I’d almost prefer that aged G6 sensor (although it’s about to come out).
Just to reiterate:
Pretty dismal post on G7. Have been thinking of going back to G6 for some time now.
My endo gave me two samples of the g7. The first one went pretty okay that second one had tons of connection problems. No way I was going to move to the g7 to drive my Mobi after seeing that.
Earlier this year the FDA in US released warning letter to Dexcom about G6 & G7, there were some changes that reduced accuracy:
https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/warning-letters/dexcom-inc-700835-03042025
…supposedly all the above issues are fixed now. Is it possible you were using an older sensor that was affected by the above?
I also was wondering if some of the missing data was caused by communication problems between the sensor and receiving device. I think G6 and G7 do different versions of bluetooth, as well as maybe signal strength differences between the 2 sensors.
The FDA warning was related to an audit, and it identified quality problems in Dexcom’s manufacture of BOTH G6 and G7.
The G7s I’ve used have varied in ages.
Incidentally I was given another G7 this week (a fairly fresh one) and may put it through its paces in a while.
Yes the missing data is inherently a communication problem. The transmitter has the data and fills it in later. The G7 has noticeably lower signal strength for a start (which has magnified issues in high-noise environments such as stadiums).