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Can hba1c be wrong?

B

BlueBerry11

Member
Messages
21
Type of diabetes
LADA
Treatment type
Insulin
Happy new year!

I was just wondering if hba1c can be wrong at all? I’ve always read that hba1c is the most accurate measurement (I know nothing is 100% accurate), but I’m wondering which measurement to trust…

My hba1c in November was 59, my hba1c in December was 55. My dexcom suggests my hba1c is actually closer to 65!

I’d love for it to be 55 obviously, but I’m worried it actually is probably closer to what the dexcom suggests…
 
Dexcom and HBAiC blood tests measure different things.
CGMs can provide an "estimated HBA1C" but as it does not measure haemoglobin in blood, it is an estimate at best.
So for an HBA1C, the blood test is more reliable.

However, this does not tell the whole story: HBA1C shows an average but this could be achieved by huge swings in BG. This is why there is increasing interest in Time In Range (TIR) which only your Dexcom can show you.

On a day to day basis, you can monitor your TIR so this is what I focus on with the view that a high TIR will provide a low HBA1C.
 
My time in range has been pretty poor due to illness and a variety of other things, so it made me think my hba1c would be much higher.

Even the difference between the hba1c in November and December is a bit strange to me…it just made me wonder whether it could be quite inaccurate. Maybe I’m overthinking it though!
 
The Hba1c is an average over 3 months, the life span of red blood cells. So your second test did not include those cells that were replaced by new cells, so you obviously had a better last month than those from the previous test that have gone.
In theory you could be rubbish at control for 9 months of the year, but very strict for the 3 months prior to your Hba1c test, and end up with a good but misleading result.
The CGM is an estimate, the Hba1c is a cell count, not 100% accurate, but very close.
 
I’ve personally never found the HbA1c that CGMs provide accurate. My actual result has always been lower than what the CGM predicts. As was said above it’s more so about your TIR rather than the actual HbA1c result.
 
As well as a time difference and healthier new cells than old now replaced ones as described above there is also the assumption of cells that last the average 12 weeks in the hba1c. If yours are slightly shorter or longer lived this will squew results as can other conditions that affect the size and shape of red blood cells.

Each diabetes test represents slightly different things so it isn’t necessarily one is better or more accurate than another. More a case of understanding what each test actually shows and what that represents as well as any limitations to it.
 
If CGM A1c estimates were correct, I'd be a walking miracle. They always estimate VERY low for me.

My lab bloods usually toggle 31<>33 (with the off dip or slight rise - nothing over 37 in 10 years), but the Libra usually has me under 20.

Personally, I look on the CGM data as showing me trends, rather than an nailed-on, accurate reflection at any given time. I prefer to look on my labs as a consistent measure I can compare each time around.
 
Thank you all!

It’s starting to make more sense, especially with the lifespan of the red blood cells. However I’m still confused with my TIR being particularly poor recently, the hba1c result being better than before. I might just accept and celebrate this however instead of trying to understand!
 
Time in range is helpful, obviously, but if your numbers have been volatile, there are likely some lows in there to buffer the highs.

Another thing about CGMs is the tend to "measure" blood glucose numbers every few minutes (I'd have to look up how often - sorry), and make a sort of best guess/likely track for the remainder, which can also impact estimated A1c scores.
 
Both my previous Dexcom G6 and my current G7 have typically forecast higher estimate HbAC1 than the actual HbAC1 lab results.
 
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