Q&A on CGM accuracy (follow-up on the G6 vs. G7)

I recently published an article titled, “Continuous Glucose Monitors: Does Better Accuracy Mean Better Glycemic Control?,” where I presented the results from wearing both the Dexcom G6 and G7 simultaneously for a month. Despite the G7’s purported “improved accuracy”, my glycemic management was worse, which I attributed to the G7’s highly erratic readings.

I got quite a bit of feedback–questions, comments and requests for more information–on why this happens, what value these so-called “accurate” readings serve, how the G7 might be used with closed-loop systems (CLS) and more.

I addressed these questions and more in this follow-up article, Q&A on CGM accuracy. (I recommend reading the first one before the follow-up, naturally.)


I’ve experienced the same issue with one g7 that I tested for 36 hours and had to return to g6 immediately. But the replacement of g7 is another updated version, which I haven’t tried yet. Dexcom might have already observed the problem and corrected it in the newer sensor versions. If only the readings accuracy would be as good as g6 overall it would’ve been the best experience. With such a short warm up period, small size, and painless insertion,plus the 12 hr grace period. Just waiting for the tandem integration to test the newer version.

Thanks for sharing this info. I read both your articles and it made me more certain that I’ll delay getting the G7, at least until I hear they’ve made some improvements. I do micro-manage and sugar surf, while also using the Tandem CIQ, and it drives me crazy when my G6 isn’t working as well as it should - i.e. at the end of the sensor life, or the end of the transmitter life…

Let’s hope some of these issues get resolved soon, for those of us who depend on the G6 accuracy but would like to have the advantages of the G7 size, etc…

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Yes Lucia I’m also still waiting for the tandem limited launch software update for the integration for g7. Only after that I’ll be able to reattempt to test the g7 again. Without pump support my TIR(80-180) drops before 97% in the last 30 days. G6 has been usually quite accurate for me. The current one I’ve, I had to Calibrate few times then second day it got better, usually something I don’t do. I was initially inserting the sensors on my abdomen but decided to insert them on the back of my arm like g7.

So, you’re saying WITHOUT pump support, your TIR is around 97%?
What exactly are your TIR patterns with and without using the pump?
Given those numbers, I can’t imagine the delta between the two is significant. I’m not dismissing it at all, but just want to clarify what you’re saying.

I’m sorry for my typing before = below. So my TIR was dropping below 97% without pump integration with g7 experiment without the ciq of tandem. But before I even started the tandem pump my dexcom g6 + mdi, i was able to achieve TIR between 90-100% it’s just depending on what I eat, activity levels, and many other variables. But the major thing that really improved quality of my life was the stability when I’m asleep. Before my BG was not as stable as with the pump usage period. That’s why I continue using the pump in control iq mode, it helps to relieve the workload up to a certain degree. I’m just awaiting the g7 integration software update to test the g7 sensor with my pump Again. Because last time I had to issues: the sensor was not reading as it was supposed to be, too low compared to actual values for 36 hrs even after calibration. And there was no closed loop with tandem since it’s not updated yet for that. I received replacement newer version of g7 sensor. I’m curious if this one measures better than the first batch.

As a Dexcom user, I find argv’s 2 articles extremely important. From his article, I learn the author’s name is Dan. In addition to being very well written, both articles clearly explain this 1 person, 1 month exmeriment. In the process, the article introduces the idea that BG levels in the body are not as consistent as I thought, with measurements sometimes bouncing in what seems like an erratic fashion. And this discussion does not even deal with the issue of CGM measurement of interstitial liquid and the lag between a change in actual blood glucose level and nearby interstitial liquid glocose level.

Bottom line – if Dan is rignt, then the value of the G6 data smoothing algorithms is considerable for those who want to quickly deal with trend changes.

Dan is carefully diplomatic in guessing that for marketing reasons, Dexcom chose to have G7 focus more on individual test accuracy instead of continuing to use G6 data smoothing to more quickly and accurately reveal trends.

This is a big deal for many of us. In the short run, though my Dexcom provider has now asked that I switch to G7, I will stay on G6 for as long as I can.

Dan is open about how a larger test with more people will be needed to prove what he has apparently found. He does not claim more than having found what is true of G6 and G7 for his body over that month. But it is important enough that I hope Dexcom developers have read his articles and Dexcom management is developing plans to research this important issue.

Yes, Dexcom is a business focused on profits, but I hope they understand the difference between single-test accuracy and a system that enables maximum ongoing glycemic control. What’s needed is more data on this issue. If Dan’s results are proven in a study, I hope Dexcom will give users, as Dan suggests, the option to build on G6’s data smoothing to reveal trends more quickly and accurately.