# Why A1c can be different from eA1c and GMI **URL:** \ **Category:** Treatment\ **Tags:** cgm, a1c\ **Created:** [September 17, 2018, 2:58pm UTC](https://forum.fudiabetes.org/t/why-a1c-can-be-different-from-ea1c-and-gmi/6491 "2018-09-17T14:58:04Z")\ **Posts on this page:** 1\ **Showing post:** 2
**Author:** ![Katers87](https://avatars.discourse-cdn.com/v4/letter/k/a9adbd/32.png) [@Katers87](https://forum.fudiabetes.org/u/Katers87)\ **Post date:** [September 17, 2018, 4:25pm UTC](https://forum.fudiabetes.org/t/why-a1c-can-be-different-from-ea1c-and-gmi/6491/2 "2018-09-17T16:25:50Z")
> [@Thanks FUD](https://forum.fudiabetes.org/t/thanks-fud/5016/4): > > if you are talking about looking at your average BG on your **meter** I’m actually talking about my Dexcom average. I recognize that that average is not perfect, but it’s actually a better reflection of my true average than my meter average. As you said, I test more when I’m out of range or think my bg levels aren’t aligned with my Dexcom. The Dex seems to be more accurate for me than it is for others on here. It’s generally behind about 15 minutes and off by as much as +/- 10 mg/dl (when considering the delay), but it’s not usually off by more than that. Though it does happen sometimes. My Dex also doesn’t consistently run lower than my real numbers (unlike others report). It’s sometimes higher and sometimes lower. > [@Thanks FUD](https://forum.fudiabetes.org/t/thanks-fud/5016/4): > > The A1C, it is not a measurement of average. So lows don’t reduce it. A1C is a measurement of the amount of glucose that has bonded to the hemoglobin. So “average blood sugar” when used to describe A1C is somewhat over-simplified While I agree that it is over-simplified, multiple studies have established that there is a correlation between the two. Based on my average glucose, the correlated A1c based on population data would be somewhere between 5.6% and 6.0% (which I fully recognize are good numbers 🙂). Some studies have shown that there can be external factors that “falsely decrease” the A1c. This creates two concerns… first, why is mine lower? Do I have one of these external factors, but I haven’t been diagnosed with it? [Pitfalls in Hemoglobin A1c Measurement: When Results may be Misleading - PMC](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3912281/) My other concern is that the studies that show that a low A1c reduces the likelihood of complications are being done on a population where there **is** a correlation between A1c and average blood glucose. I think. So, is my A1c truly representative of how much glycation is occurring on other proteins in my body? Or since my red blood cells aren’t living as long as they are for the general population is my average actually a better measure of how many AGEs I’m accumulating? I think my average is fine, so I’m more worried about the first concern. Both are something I would like to know though, especially because while my average is fine now it hasn’t always been this good. I think my A1c has always been lower than my average glucose would predict it to be. > [@Thanks FUD](https://forum.fudiabetes.org/t/thanks-fud/5016/4): > > You can get somewhat of a ballpark idea of your RBC lifespan by getting your reticulocyte count and doing the calculation. It is still a ballpark, but it can give you a little better guess of your RBC lifespan, and how it might compare to normal lifespan. Thanks for the tip. I’ll ask for this next time I see my doctor. --- _[View the full topic](https://forum.fudiabetes.org/t/why-a1c-can-be-different-from-ea1c-and-gmi/6491)._