Glucose Management Indicator (GMI) on Libre reports - conflicting info?

[PerSpinasAdAstra]

I wonder if some of the effects of metformin would linger if you tapered off and stopped taking it. Like if it has made your body more insulin sensitive and reduced liver glucose production then your body having healed to an extent would carry on like that (providing that you didn't mess it all up by eating the wrong things obviously). I have found that intermittent fasting and even 10mins of brisk walk 30mins after each meal really helps to reduce insulin resistance, which was getting quite bad when I was injecting insulin (which I didn't need).

I don't think the effect would linger very long unfortunately. To the best of my understanding Metformin is basically a very mild mitochondrial 'poison' - once it's flushed out of the body it quickly 'recovers' from the effects. It has an elimination half-life from the blood of around 18 hours, so within a week of stopping it the amount left in the body is miniscule. After two weeks it would be basically gone. I don't imagine there would be a significant effect much beyond that - at least not one what could be observed on a Libre 2 graph.

 

[Lucyr]

No, below that there is a converter from average glucose to A1C, other converters on other sites give me the same figures:
View attachment 30240
Then compared with the estimated A1C in LIbreView (based on the GMI) it's quite a bit higher, gives 42 A1C there but 36.7 above.

I’m not sure why you need to use a converter anyway, but just use the top one then if that agrees?

 

[Lucyr]

Still think it must be that you’re doing something wrong though, they agree for me.

Libres formula would also agree. (6.2 +2.59) / 1.59 = 5.5%.

Can you show your libre screenshots where the 90 day average bg is 6.2 and the a1c is 42? Then we can see what’s causing the confusion?

 

[rebrascora]

Libre gives me an average of 6.5 over 90 days, which is predicted by Libre to give me an HbA1c of 39 and putting it into that (red forum) calculator gives me a predicted HbA1c of 38.8 which is essentially 39, so Libre and that red forum calculator seem to be in agreement for me too . My actual HbA1c is generally 45-53, so I think they are both overly optimistic for my body.

 

[PerSpinasAdAstra]

For me, following use of a single sensor for two weeks, the 'Estimated A1C' number in the LibreLink app (33 mmol/mol) roughly fits with the 'Average Glucose' number in the app (5.6 mmol/L) when using the calculator on the red forum, but does not fit with the Glucose Management Indicator (GMI) number from the 2 week report generated from LibreView (39 mmol/mol). Presumably there are different formulas used for the A1C number in the app and the GMI number in the LibreView report - which may be the cause of the confusion?

 

[rebrascora]

Yes, I am guessing that there will be some way to factor in the shorter period of data for HbA1c estimation, if it is less than the 90 days.

 

[Lucyr]

Presumably there are different formulas used for the A1C number in the app and the GMI number in the LibreView report - which may be the cause of the confusion?

The website gives the same formula as the app

 

[helli]

Yes, I am guessing that there will be some way to factor in the shorter period of data for HbA1c estimation, if it is less than the 90 days.

But does that make sense as a thing to do?
The way I understand it (which may be wrong), HbA1C measures the glucose attached to haemoglobin which stays attached for about 90 days. What does HbA1C mean over a shorter period when it is not something that can be measured.
This doesn’t mean GMI is an irrelevant number over the shorter time period but it does mean it is less likely to be a “good” representation of your HbA1C.

 

[PerSpinasAdAstra]

I just looked it up (though it's probably in the thread I linked earlier). The formula for the GMI, expressed in mmol/mol appears to be: 12.71 + (4.70587 × [mean glucose in mmol/L]). It's a different formula than the one used for the A1C number in the app, and when I plug in my numbers I get 39.

Here's where I got the GMI formula from - appears under Table 1:

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 ...

www.ncbi.nlm.nih.gov

Edit: - And when I use the formula in the screenshot from @Lucyr I get 5.15%, which converts to 32.8. Can we move on now? 😉

 

[Lucyr]

Yes, I am guessing that there will be some way to factor in the shorter period of data for HbA1c estimation, if it is less than the 90 days.

I’d guess that the person seeing a different a1c in libreview vs the app had a different time range selected as it is the same formula. For example 1 week in libre view and 2 weeks in the app.

Abbot publish the formula, it’s a standard simple formula, it doesn’t account for only having 2 weeks instead of 90 days because it doesn’t need to, since time isn’t part of the formula.