Accuracy of A1c test

I recently had an A1c done at my internist. It was higher than I thought it should be (I use a Dexcom CGM). Then I went to my endo and had another A1c done (about 5 weeks later). It was one full percentage point lower and much more inline with my Dexcom. The endo’s office said they have had this happen with other patients with A1cs done at both of the places with that much or more of a variance. So how accurate are these tests anyway? I wonder if they’re even worth getting or maybe I should just go off my Dexcom.


This is interesting information. I too would be interested to see if anyone else has had this experience.

I have had the same problem in the past. Any labwork has inherent flaws because you are just sampling a few blood cells out of many, many cells floating around your body. Samples can be affected by how they are handled after being drawn too. That is why I don’t put too much stock in my A1C, especially if I’m just dealing with small differences (1.5% in either direction). Also, A1Cs are affected by lows. So you can have a great A1Cs, but a HUGE range in BGs. Personally, I pay more attention to my daily BG readings, as (for me) these more accurately reflect how I’m doing.

A man with one clock knows what time it is. A man with two clocks is never sure.

In my local area there are two main labs (Labcorp and Quest). Reference ranges for A1C differ at these two labs by about 1.0. And (surprise, surprise) so does my A1C between the two labs. So comparing between the two when we’re talking about small changes is impossible.

Maybe one or the other is as accurate as our meters!
I think the Dexcom is the most accurate of all if you have done your controls during a steady state. How to get BGs into the target zone all in the palm of one’s hand. A WONDERFUL gadget. May their stock do well.

No, you’re missing my point. I realize there can be a difference in A1cs that are done 5 weeks apart. I know that. But what I’m saying is that the A1c done first was NOT inline with my Dexcom report, while the 2nd A1c was more inline with my Dexcom report.