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GMI

p4ul

p4ul

New Member
Relationship to Diabetes
Type 2
I've mentioned a couple of times that I'm wearing a G7 to monitor the effects of my usual diet on my BG levels. Results have been interesting to say the least.

One useful side feature of the G7 is a measure of GMI%. It seems to carry some fairly reputable weight behind it, although I can't find much from the UK:

Glucose Management Indicator (GMI): A New Term for Estimating A1C From Continuous Glucose Monitoring - PMC

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 ...
pmc.ncbi.nlm.nih.gov pmc.ncbi.nlm.nih.gov

“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.”

My GMI reading from the last 8 days is 6.1, which apparently would correlate to a HbA1C of 36mmol/mol. I'd be pretty delighted if this were a decent approximation, so I wonder if anyone has any experience of the accuracy of GMI?
 
p4ul said:
My GMI reading from the last 8 days is 6.1, which apparently would correlate to a HbA1C of 36mmol/mol. I'd be pretty delighted if this were a decent approximation, so I wonder if anyone has any experience of the accuracy of GMI?
Click to expand...
I’d ignore it. GMI is just a formula applied to your average blood sugar. It’s not the same as a hba1c which measure the glucose on your actual blood.

Rather than using average blood sugar adjusted by some formula to approximate a hba1c, just look at your average blood sugar, and how the average and the distribution change over time.
 
My Libre estimated HbA1c from the GMI is usually lower than my actual one by a few mmols (ie 43 and I get a result of 46mmols) but my last result was spot on with my actual result. Some people find that it reports lower and some people find it reports slightly higher.
I believe @Docb was collating people's results on a thread somewhere.

I think it will be impacted by things like if you have suffered any/many compression lows and how your CGM compares to finger prick readings. My Libre usually reads lower than a finger prick (in range) but of course I have no real way of knowing if my Libre or my BG meter reading is closer to the real value. The fact that the estimated Libre HbA1c is usually lower than my actual HbA1c suggests my BG meter is nearer correct and Libre genuinely does read slightly low for me, but I may be missing something in assuming that.
Obviously with the G7 you can calibrate it, so depending upon how often you calibrate it and if it is always in the same direction, that might give you a possible indication of whether it will be near correct.

I certainly wouldn't rely on that result being correct and perhaps relax your efforts to manage your diabetes based on it and then find your actual result is higher and you have lost ground with your management as a result.
 
My experience is that the GMI (or estimated HBA1c) is a useful measurement to track my overall diabetes management over time but not an accurate indicator of HBA1c.
The last time I checked, my CGM was estimating a GMI which was more than 20% lower than the HBA1c that was taken the same week.

As to whether you will find it useful, it depends what you are using it for. As a guestimate of your HBA1c, it will give you an indication of the ballpark but it is not a prediction of the true result. In your shoes, I would not expect a HBA1c of 36 (although it could be), but if your GMI was 60 a month ago, it would be a great indication that things are going in the right direction.
 
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Just for interest, there was a whole thread dedicated to comparing Libre GMIs with people’s HbA1c here. You can see that some people's are closer than others. I imagine results from the G7 might be similar.
mashedupmatt

Thread 'Libre HbA1c v Actual HbA1c'

Interested to know how accurate everyone's Libre guesstimates are against actual blood results - mine was 5 mmol/mol higher on blood test to what Libre was saying - admittedly I don't pay too much attention to what it calculates but would be interested to know others experiences...
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Dexcom had pairs of HbA1c and 24hr glucose data, and then worked out a ‘best fit’ formula that can be used to estimate what your glucose profile might be as an HbA1c. But of course there are lots of ways in which this may not be right for you.

This was the formula they derived (I seem to remember it was in the app somewhere).

GMI mmol/mol = (4.70587 x CGM average mmol/L) + 12.71

They can be helpful, but don’t be surprised if the estimate GMI is not what you get at your next HbA1c.

I think that’s one of the reasons they opted to use the term Glucose Management Indicator, rather than describing it as HbA1c.
 
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