The latest version of clarity that shows expected a1c doesn't match my last a1C

my last A1C was 5.4 which is the lowest it has ever been. I’m not sure it was an accurate result from the lab that I always go to. I just downloaded the new version of clarity and saw that clarity expects my a1c to be 6.1. I get another lab test in about three weeks so we will see

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I didn’t realize that was back. I recall they had to remove it. Gonna have to go see what it says for us now.

cut-n-paste from Clarity

Release notes for March 27, 2019

  • Added Glucose Management Indicator (GMI) to Overview and Compare reports. GMI approximates the laboratory A1C level expected based on average glucose measured using continuous glucose monitoring (CGM) values derived from at least 12 days of CGM data.

EDIT2: Clarity shows 0.4 points higher than our last actual A1c over the 90-period which I expect the A1c to be covering.

BTW - Dave, thanks for the FYI that this was added.


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How do you get an accurate 90 day average BG calculation? I can average successive 30 day averages from my CGM but even those readings are not that accurate. Also the A1c is weighted towards the last 30 days.

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It didn’t matter if I set it to 30 or 90; the result is the same: 6.1.

As per your comment, it seems current “wisdom” is that A1c is indeed more influenced by the last 30 days than the 60 days previous to that. As you know, “knowledge” varies according to the whims of the universe (and the “latest” studies"). Witness “eggs are OK”; vs “eggs will kill you prematurely if you eat more than 3 a week”. Who the heck knows? The only thing I can say for certain was that the old wive’s tale about staying out of the water for a hour after eating, was totally, utterly FALSE. I even figured that out on my own when I was a little kid. I didn’t need a degree in physiology or anything else for that matter, to know what a crock that “fact” was.

I just Googled “a1c for 116 average blood glucose”, went to one of the results which was at Accucheck. There, I inputted 116 in the calulator. Result? A1c of 5.66. Like I alluded to previously, I don’t think there is a lot of uniformity, or agreement, if you will, as to what a particular average glucose is going to result in an A1c of “x”. I suspect it depends on the lab, and even what the random blood glucose at the time of draw was, and the moon phase. I’m eager to see what my A1c result will be in 3 weeks and how closely it will match Clarity. I’d be a lot happier if my average A1c was closer to 100 but 116 isn’t too awful, I suppose.

[EDIT] If I seem confused, cut me some slack–my sensor says I’m 55. LOL! I think I’ll go test and maybe eat. later, dudes, and dudettes. Back. meter said 59.

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FWIW mine also is 6.1 regardless of selecting the time frame. My last A1C at the end of January was 5.6. I have another test in two weeks so we will see how it compares.

If I’m not mistaken all of these apps use a fairly standardized exponential moving average algorithm. When comparing one app result to another, one may weigh the past 30 days average blood glucose more or less than another.

I’m using Sugarmate Glance, and it’s telling me my estimated A1C based on 90 days of CGM readings is 4.5 (average 90 day BG 4.6 mmol/L or 83 mg/dl). We’ll see in another 6 weeks when I get re-tested. :thinking:

For what it’s worth, Clarity (the EU version, not the US) has always shown my A1c to be about 1% lower than the lab result.

Here’s more info on the Glucose Management Indicator (GMI) number that’s now part of Dexcom’s Clarity reports. From Diabetes Care, November 2018.

While A1C is well established as an important risk marker for diabetes complications, with the increasing use of continuous glucose monitoring (CGM) to help facilitate safe and effective diabetes management, it is important to understand how CGM metrics, such as mean glucose, and A1C correlate. Estimated A1C (eA1C) is a measure converting the mean glucose from CGM or self-monitored blood glucose readings, using a formula derived from glucose readings from a population of individuals, into an estimate of a simultaneously measured laboratory A1C. Many patients and clinicians find the eA1C to be a helpful educational tool, but others are often confused or even frustrated if the eA1C and laboratory-measured A1C do not agree. In the U.S., the Food and Drug Administration determined that the nomenclature of eA1C needed to change. This led the authors to work toward a multipart solution to facilitate the retention of such a metric, which includes renaming the eA1C the glucose management indicator (GMI) and generating a new formula for converting CGM-derived mean glucose to GMI based on recent clinical trials using the most accurate CGM systems available. The final aspect of ensuring a smooth transition from the old eA1C to the new GMI is providing new CGM analyses and explanations to further understand how to interpret GMI and use it most effectively in clinical practice. This Perspective will address why a new name for eA1C was needed, why GMI was selected as the new name, how GMI is calculated, and how to understand and explain GMI if one chooses to use GMI as a tool in diabetes education or management.

For more than 10 years I have noted that my A1c floated about 0.5% above the A1c predicted by my average glucose CGM data, a discordance. I recently discovered that I had iron-deficiency anemia and I found a study that documented people with anemia often reported A1c’s about 0.5% above what their CGM average predicted. When I supplemented iron, my next A1c aligned much better with the CGM average predicted, only off by 0.1%.

Now Clarity reports this new indicator, the GMI or glucose management indicator and it is about 0.6% higher than my average glucose would predict.

I think we need to see the GMI, A1c, and CGM metrics like time-in-range, percent hypo, coefficient of variation (standard deviation/mean glucose expressed as a percentage) and average glucose as approximate indicators of our glucose management. When all of these metrics are examined together, we can get a good idea about how well our management tactics are working. It’s not as precise as we would like but still useful.


Thanks for sharing @Terry4. It must be nice to see your A1c fall like that!

The GMI on my Clarity report is also much higher than my average glucose predicts. It’s also much higher than my last A1c. I wonder if this value aligns for anyone?

Even though I’ve told myself that my discordant A1c did not reflect accurately my glucose experience, it is nice to observe data that affirms all the effort one makes.

As a student, when you work hard and then receive a good grade, it reinforces your behavior. When you work hard and get a mediocre grade, it can be demoralizing. I think the same holds true with the A1c.

When my A1c is in agreement with my glucose experience, I like the fact that the doctor can see independent confirmation of my CGM experience. I then know that the doctor shares my perspective on this issue.

The issue of physician hyper-phobia about hypoglycemia is another matter. My normal A1c makes most clinician’s nervous. That’s OK since I know better!

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My Sugarmate GMI 5.3 is 0.7% higher than my mean (Average) blood glucose. For my metabolism, there’s little correlation between estimated A1C (eA1C) and the glucose management indicator (GMI).

I know my A1C will be lower than the 4.7 tested in November, the question will be how much lower.

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