Why A1c can be different from eA1c and GMI

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How about if someone has Thalassemia, an inherited blood disorder where red blood cells are smaller than normal and can cause severe anemia? Would that also cause an a1c discrepancy - increase or decrease?

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Thalassemia shortens RBC lifespan, so it would reduce A1C.

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23

Ah, thank you! Maybe that is why I can achieve an a1c of 4.9 :frowning:

Confusing because my lab a1c is consistently higher by 0.3 than my a1c as calculated by xDrip+ / Dexcom which just uses the CGM BG avg values, not the actual glycosylated hemoglobin as in the lab test:

ā€œA1c:ā€ + (Math.round(10 * (avg + 46.7) / 28.7) / 10d) + ā€œ%ā€;

24

I think the CGM estimates are not very reliable for many people.

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25

True, that is the case for me for some percentage of the time, for sure. :frowning:

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26

I am sure the numbers would not change significantly. If you are achieving a 4.9 with RBCā€™s that live only 10 weeks, it would certainly not jump up to anything horrible if they lived 15 weeks. The 4.9 is a reflection of your good control.

Also, since you run a lot, your hematocrit and hemoglobin may be lower than normal, because running has increased your blood plasma volume.

Donā€™t worry too much if you see lower numbers there. I think you are in great shape. Keep doing what you are doing.

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27

Yes, they usually are, too!

Thank you, I appreciate this!! :sunny:

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28

Google ā€œRunnerā€™s Anemiaā€. Take it as a sign that you are kickinā€™ it.

Also, check out your blood counts and your A1C after a hard training period, about 10-14 days after a race. See how it drops. That is a badge of honor. Wear it proudly.

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29

Oh, wow, I hadnā€™t heard of that before. Next endo appt is April but hope to have annual physical in Mar! Iā€™ll aim for that time frame to see how the CBC looks!

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30

I found this googling Runnerā€™s Anemia ā€¦

One effect of regular endurance exercise is that it produces an increase in red blood cell mass and plasma volume

I didnā€™t realize thisā€¦ No wonder I feel so much better w/ nice, long runs.

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31

I think one of the other effects of thalassemia is that your body will counter the misshaped RBCā€™s by creating more of them.

As discussed earlier in this thread, possibly this could lower A1C, at least in theory.

Have you been checked for thalassemia?

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32

Yes, I learned I had it when I was young. Initially thought to be just anemia but further tests showed it was thalassemia minor.

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33

I am confused that my G7 90 day GMI reads 5.8 with an average glucose of 102. If I go to one of the many A1C calculators on the internet, it says an average glucose of 102 would calculate to an A1C of only 5.18.

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34

Hi @egb01l. Welcome to FUD!

Dexcom has their own calculation they use for that.

Realistically, your BG can go up faster than what your Dexcom shows. It takes a while for the Dexcom to catch up. For that reason, they may be giving you a slightly higher number than just using the BG average.

And one other thing to mention - your A1c is not the average of your BG. It is a measurement of how much time you spend with high BG, and how high it is. That is not the same thing as an average.

In other words, with an average, low numbers counter-act high numbers. For example, the average of 180 and 40 is 110, right?

But with A1C, a low does not take away the time you spent high. That 40 did not take anything away from the time you spent at 180.

Does that make sense?

People just say ā€œaverageā€ because they donā€™t understand what A1C is truly measuring, or itā€™s just easier to say ā€œaverageā€ instead of explaining it.

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35

Thanks Eric! Very interesting. That is by far the best explanation Iā€™ve gotten. So are these A1C calculators absolutely worthless? Also, my BS is usually somewhere in the mid 90s during sleep and the first hour after I awake. Then it drifts up to around 110 by the time I eat my first meal around noon. It NEVER goes above 130 after a meal but it often sits at 115-120 during my long hours between lunch and dinner. Does that sound like an A1C of 5.8? My last A1C from the lab was 5.6. Thanks in advance, I eat very clean and am really trying to understand whatā€™s going on here.

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36

I donā€™t think they are worthless. They can give a person a general idea of how a particular A1C number translates to a personā€™s BG number.

As long as you understand that they are just using a formula to give an estimate, rather than doing a lab measurement of how a personā€™s hemoglobin has become glycated over time.

If you know the context, it can be a useful tool to interpret your numbers.

Itā€™s hard to say. There are a lot of different possibilities. There is the accuracy of Dexcom, how long your red blood cells live, what your BG was like in the weeks prior to the test, etc.

A person whoā€™s red blood cells live longer will generally show a higher A1C result than a person with the same BG numbers with shorter living red blood cells.

And different things can affect how long your red blood cells live.

Every A1C test result or A1C estimate should be viewed with and understanding of all the variables.

37

Here are the comparisons between A1c and GMI, they are not the same.

GMI vs A1c

Real World A1C and GMI studies

38

I learned that when I had chemo in 2013. Lowest ever A1C of 4.6.

The only good thing about chemo!

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39

Great explanation!!

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