I've often used that Chris Kresser article to explain away my slightly high A1c but I have read other reasons mentioned in various diabetes articles, like this one. Not a perfect marker for many reasons.https://blog.designsforhealth.com/hemoglobin-a1c

In my mind it is another blood marker that as long as it is in/near range, as my doctor explains, it means that "MY Normal" in my lab runs higher within their range. It may be influenced by my LC diet or for no particular reason. My lab uses 5.6 as the cut off for "normal" and 6.4 for diabetes. In the past 5 years, tests have been 5.6,5.7,5.9,5.8,5.8 and recent 5.1 (no idea why, but not concerned either way it goes if it stays near my average).

At the same time this blood is drawn for standard lab tests, another is run through an on-site machine for all the blood markers usually checked before a chemo infusion. Most recent test, the oncologist surprised me by saying I have the healthiest blood in his entire practice, whatever that means He plotted the WBC (total breakdown was over 100%), RBC (mid-high), hemoglobin and hemocrit. All mid-range but together the total pattern was considered very healthy to his brilliant mind. If it weren't for an annual cancer check-up, I would be like Jean and not get any blood tests anymore. I haven't been to the GP or Dr. Westman since I turned 65 three years ago, the oncologist visit is more than enough.