September 13, 2005
A1c (Glycohemoglobin, HgbA1c)
Question from Northern Coastal California, USA:
In the literature regarding A1cs, I’ve seen it stated that it is an average over the past two to three months. Yet, I also have read that “glucose binds irreversibly to hemoglobin molecules.” So, will only one episode of hyperglycemia lasting only hours just prior to the test cause the A1c result (which represents two to three months of control) to be disproportionately higher due to irreversibly saturated hemoglobin, or is it truly an average of the longer time period? To rephrase, what if I have good control for three months and then have high blood sugar the week before the test? Will the results reflect an average, or will it appear that my blood sugar has been roughly as high as the recent hyperglycemic week?
Answer:
I like to think of the A1c test like an M & M candy coating — every time your sugar rises, it coats the surface of the red blood cell. The thicker the coating, the more episodes of high glucose over about half the life of the cell (about two months). So, it is the accumulation it is measuring over the entire time.
JS
