What is the Hemoglobin A1c Test?

Hispanic girl testing her blood sugar
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Hemoglobin A1c Test - Definition

The A1c test (also known as HbA1c, glycated hemoglobin or glycosylated hemoglobin) is a blood test that correlates with a person’s average blood glucose level over a span of a few months. It is used as a screening and diagnostic test for prediabetes and diabetes. It is also used to monitor blood sugar control for people with diabetes, both type 1 and type 2.

What is A1c?

The A1c test measures how much glucose is stuck to your hemoglobin, or more specifically, what percent of hemoglobin proteins are attached to glucose.

So if you have a 7% A1c, that means that 7% of your hemoglobin proteins are glycated (have sugar attached).

Once glucose sticks to a hemoglobin protein, it stays there for the lifespan of the hemoglobin protein, or for about 120 days. That's why, at any moment, the glucose attached to your hemoglobin A protein reflects the level of your blood sugar over two to three months. Why this period of time? That is the lifespan of a red blood cell. The hemoglobin gives your blood its red color and it is carried inside the red blood cells. They are produced continuously by your bone marrow and, on average, live for 120 days before they have lived out their useful life and they are removed by the spleen.

What Do the A1c Test Results Mean?

For a person without diabetes, a typical A1c level is about 5%. Increased levels of A1c can show that you have prediabetes or diabetes. Often these conditions have no symptoms and the A1c test is the first indication that you have diabetes.

InterpretationA1C Level
Normal5.7% or less
Prediabetes5.7 to 6.4%
Diabetes6.5% or above

The American Diabetes Association recommends A1c testing at age 45 if you are overweight or obese, and repeated testing every three years. If you have a level showing prediabetes, you should be retested each year.

A1C Test Levels in Diabetes Monitoring

If you have diabetes, it's recommended by the American Diabetes Association that you have the A1c test twice per year if you are meeting your treatment goals, or as often as four times per year until you reach your recommended levels.

Your A1c target may be individualized, but studies show a target of below 7% reduces risks of diabetes complications. That is the level recommended by the American Diabetes Association.

How is the A1C Test Done?

The hemoglobin A1c test may be done on a blood sample drawn and sent to the lab, or it may be tested in the doctor's office. If you have been diagnosed with diabetes, you may use a home test kit for A1c. This is not recommended for screening if you haven't been diagnosed with diabetes.

How Does the A1C Test Compare to Blood Glucose?

In order to compare A1c with blood glucose test numbers, the Average Glucose (eAG) number may be calculated and reported. This may become more standard usage in the future. It is a simple numerical calculation that may be done automatically and reported on your lab results.

Sources:

The A1C Test and Diabetes, National Institute of Diabetes and Digestive and Kidney Diseases, March 2014.

Hemoglobin A1c, Lab Tests Online, American Association for Clinical Chemistry, December 30, 2015.

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