Glycosylated hemoglobin

If you don't know what this is, chances are good that neither you nor your near and dear have diabetes. This test, also known as hemoglobin A1c or HbA1c, is a measure of how much glucose your iron-containing hemoglobin molecules are carrying.

Over the course of the 120 day lifespan of a red blood cell, the hemoglobin within binds irreversibly with glucose, forming glycosylated hemoglobin. The higher the level of glucose in the blood, the greater the fraction of hemoglobin A all gummed up with sugar. Although a little junk food binge would be immediately reflected in subsequent blood sugar measurements, it would take 2-4 weeks of binging to affect the HbA1c levels.

For that reason, HbA1c is used to monitor long-term success in the treatment of diabetes. It is not used to diagnose diabetes; the disease is defined by elevated fasting glucose levels or an abnormal glucose tolerance test. Boston researchers* using data from the Women's Health Study, however, have found that elevated HbA1c levels even though still within the normal range are potent predictors of future diabetic risk.

Over 26,000 women age 45 and older with baseline A1c levels of 5 (ideal is <6% and goal for diabetics is <7%) were followed over 10 years for the development of diabetes. Relative to the old gals who maintained A1c values of 5, those who dinked above 5.5 but less than 6 had three times the diabetic risk; this risk rose 29-fold for those between 6 and 6.4 and the women above 7% had 81 times the risk which pretty much means they became diabetic.

Dr. Aruna Pradhan and colleagues issued the usual bland sort of 'needs further study' statement: Although these data do not support the use of HbA1c as a single measure of diabetes risk, our results do suggest that the prognostic significance of elevated HbA1c may warrant a greater emphasis in primary prevention.
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Am J Med 2007;120:720-727.