Hb1Ac is generally measured in mmol/mol, although often also in percentages.
What I don't get is why the mmol/mol isn't simply a tenfold of the percentage. mmol/mol basically means 1/1000th right? And percentage means 1/100th. Or am I missing something?
Molarity is a concentration based on a molecular weight. Without knowing the actually number, I assume glycosylated hemoglobin has a higher molecular weight than non-glycosylated hemoglobin, so you can't just divide by 1000. Percentage doesn't account for differences in weight and thus is a straight ratio of one to the other. That is why the two measurement don't exactly match.