Mechanics of hemoglobin glycation
Let's say a person has a well controlled blood glucose level of 125 mg/dL (no major spikes or valleys) and his A1c test comes back as 6.0. Right on the expected numbers.
Two days after his last A1c test he eats a bunch of candy and his blood glucose goes up to 225 mg/dL for 2 hours, then tapers off to his "normal" of 125 mg/dL over the next 2 hours.
What would his A1c be 2 days after the candy binge? One week after the binge? One month after the binge?
Basic question is how long does it take to glycate hemoglobin to the 7% (or 8%) level with at a blood glucose level of 225 mg/dL?
The reason I ask this is that I believe the description of A1c as being the "average" blood glucose over the past 2 - 3 months is a fallacy. It is a convenient way to express it, just as saying the sun rises in the east is a convenient way to express the solar phenomena. But we know the sun doesn't orbit the earth, it is the earth's rotation that makes it appear to do that. The sun doesn't "rise". The earth rotates so that our position on it "slides under" the sun.
My contention is that A1c is more dependent on how high a person's last spike was, how long that spike lasted, and how long after that spike the A1c test was taken, NOT the "average" blood glucose over the last few months. But it's a lot easier to say "average" than all the rest of that.
For a person without significant spikes in their blood glucose level their A1c will appear to be the "average" over the past several months because there has been no significant deviations from that average. With significant deviations all bets are off.
Yes, I have seen the study where the currently used formula AG = (28.7 X A1c) - 46.7 was developed. It appears that study was based on subjects with well controlled blood glucose, i.e. no significant spikes. In fact, IIRC, the subjects primary physicians were encouraged to monitor and maintain control over the subjects blood glucose. Under those conditions the A1c will be more indicative of average blood glucose by design.
I have asked these questions of several diabetes "experts" and have a couple of inquires out now which haven't been answered yet. My own PCP answered with a curt, "A1c is what's used as the international standard to indicate "average" blood glucose. That's what I use." Period. Other more open minded folks have said, "That's a good question. I don't think it's been asked before. Why don't you see if you can find out?"
Can you answer (or find an answer to) my "Basic question" above?