HbA1c has been discussed in many threads. However there are aspects of it that I am still puzzled about and I would be interested in any light that can be thrown on the subject. I don’t think it makes much difference to treatment, at least in my case, so my interest is really “academic”. It is said that HbA1c indicates the average blood glucose level over a period of about 12 weeks because that is an average time for the red blood cells to be replaced. Not everyone’s RBCs keep to the 12 weeks, so comparing one person’s HbA1c with another may not be appropriate and HbA1c may not agree with an average blood glucose calculated from regular blood testing. 1. Does anyone know, how the red blood cells becoming glycated but continually renewing, can be represented mathematically, to make it possible to calculate what effect different renewal rates would have on HbA1c? 2. It is also sometimes said that the period before the HbA1c test, maybe 4 weeks before, has more significance than the earlier period. Is there any evidence for this or is it perhaps a consequence of the above maths? If it is true and as long as your RBCs renew on average in more than 4 weeks, doesn’t that largely negate the argument that different renewal rates affect HbA1c?