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March 2, 2006

A1c (Glycohemoglobin, HgbA1c)

Question from Montreal, Quebec, Canada:

On the net, I see many people with diabetes saying that the A1c is not a true reflection of how good their glucose control is. They say that their A1c might show a good control (less than 7.0) when, in fact, their glycemic day to day indicates many highs or many lows that affect the A1c one way or the other. Is this a myth? Can you trick the A1c which shows an average of the glycemia over a three month period? What about someone who has large fluctuations of glycemia on a day to day basis ?


Remember that the A1c is a measure of your average blood sugar over the last three months. It is not a simple mean, but it is an arithmatic mean. A simple mean implies all the numbers over the time contribute equally to the mean result. An arithmatic mean indicates that the values over the last month impact the A1c value more than those two months ago, etc. The other issue is that there are highs and lows causing difficulty in truly evaluating a trend. At present, the hemoglobin A1c is the best test we have for measuring glucose control. There are problems with it. Many are looking at how the values compare from one laboratory to another with different methodologies and no uniform standard for comparing between laboratories. Anyone who has premature destruction of red blood cells can have falsely low levels. Some who have hemoglobinopathies may have false elevations.