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January 25, 2004

A1c (Glycohemoglobin, HgbA1c)

Question from New Delhi, India:

I read one of the articles on a particular diabetes website where they had mentioned the various blood plasma glucose values and their corresponding Hba1c results. Quite naturally they had mentioned higher Hba1c values for high blood plasma glucose levels and smaller Hba1c values for the latter. In a lab result of mine, my post breakfast blood sugar level was 133 mg/dl [7.4 mmol/L] and the corresponding Hba1c value was 5.9%. Also I have the mathematical means of converting the whole blood glucose value into the plasma blood glucose value and further convert it into the Hba1c result. Does this mean that I will derive different Hba1c values from either my fasting blood sugar level or the post-breakfast one? Please guide me on this.


From: DTeam Staff

Plasma glucose is the “currency” for discussing glucose values. Most meters now correct for blood glucose and display the calculated plasma glucose value. HbA1C is really meant to reflect your average blood sugar over the preceding 3 months. It is not a simple mean but is an arithmetic mean such that your more recent values impact the final value more than the most distant results. Clinically, we use the three month time cut as a guide for the frequency of evaluating patients. The conversion of mean plasma glucose from the HbA1C (the regression equation) was originally published in an article in the early 1980s. It is meant to be a mean of all pre-meal and post-meal values. That is why the mean value always looks a little higher than the fasting or pre-meal values you obtain from your meter. If your doctor did both a plasma glucose and an HbA1C at the same time, there may be differences in the trends as the fasting glucose value is an isolated time point and the HbA1C reflects the previous three months. It sounds like your sugars are under good control.