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What is the HbA1c test?

The HbA1c test (hemoglobin A1c test, glycosylated hemoglobin A1c test, glycohemoglobin A1c test, or A1c test) is a lab test which reveals average blood glucose over a period of two to three months.  Specifically,  it measures the number of glucose molecules attached to hemoglobin, a substance in red blood cells.

The test takes advantage of the lifecycle of red blood cells.  Although constantly replaced, individual cells live for about four months.  So by measuring attached glucose in a current blood sample, average blood sugar levels over the previous two to three months can be determined.

HbA1c test results are expressed as a percentage, with 4 to 6 % considered normal.  The HbA1c "big picture" complements the day to day "snapshots" obtained from the self-monitoring of blood glucose (mg/dl), and the two tests can be equated as in the printable diabetes chart.

When interpreting your hemoglobin test you should keep in mind that results differ depending on the test method used.   Some labs measure hemoglobin A1 (which is different than hemoglobin A1c).  Also, realize that HbA1c results may reflect the averaging of a period of high glucose with a period of low glucose, as opposed to the consistent readings required for good control.  To best understand your  HbA1c results always consult your healthcare professional.

To view a list of popular diabetes guide books with more information about the HbA1c test, blood glucose and related topics click here.

If you are interested in a simple means of tracking your ongoing HbA1c range you can download the Diabetes Chart HbA1c Tracker.


American Diabetes Association. American Diabetes Association Complete Guide to Diabetes. Alexandria, VA: American Diabetes Association, 2005.
Beaser, Richard S., M.D., and Amy P. Campbell. The Joslin Guide to Diabetes: A Program for Managing Your Treatment. New York: Fireside Books, 2005.
Zerhouni, Elias A., "
Report on Closing the Disparity Between Hemoglobin A1c Treatment Guidelines and Practice," US Department of Health and Human Services, National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, 2007: 6-7.

Page created September 14, 2000 and last updated August 3, 2011

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