I would like to know more about the A1c test. What is it? What does it test for? How does it differ from the glucose tolerance test? Is the A1c test considered to be the “final authority” on determining if one has diabetes or not? What is the normal range for the A1c test results?

Hemoglobin A1c is a test developed in the 1970s as an index of overall glucose levels for the previous several weeks-months. It represents glucose attached to the protein hemoglobin in the red blood cells. Since the life span of a red blood cell is approximately four months, the time-average representation of A1c (also called glycohemoglobin, glycated hemoglobin, or glycosylated hemoglobin) gives an estimate of glucose levels. It is not as specific as a blood glucose level and so isn’t as helpful for diagnosis of diabetes. There are some studies where it has been tested for making the diagnosis.

Usual A1c levels are approximately 4-6%, but each lab has slightly different values. There is some attempt to standardize the test, but this is not yet the case. You should talk to your physician and diabetes team since they can answer this question for the specific lab they use and also tell you how to judge what A1c level represents what range of glucose values.

We believe that the A1c should be tested about every four to six weeks in young children and anyone with difficult-to-control type 1 diabetes. The American Diabetes Association suggests a minimum of every four months for type 1 and also for type 2 diabetes.

The DCCT tested A1c levels every four weeks. Unfortunately, most people with diabetes in the USA do not get this done more than once a year — and so do not have any feedback on their degree of glucose control.

SB

[Editor’s comment: The A1c is not the “final authority” on determining if one has diabetes, and, as you can see, it differs greatly from a glucose tolerance test.

SS]