Definition

HbA1c is a test that measures the amount of glycosylated hemoglobin in your blood. Glycosylated hemoglobin is a molecule in red blood cells that attaches to glucose (blood sugar). You have more glycosylated hemoglobin if you have more glucose in your blood.

The test gives a good estimate of how well diabetes is being managed over the last 2 or 3 months.

Alternative Names

Glycosylated hemoglobin; Hemoglobin - glycosylated; A1C; GHb; Glycohemoglobin; Diabetic control index

How the test is performed

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants and young children, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.

How to prepare for the test

No special preparation in necessary.

How the test will feel

When the needle is inserted to draw blood, you may feel moderate pain, or only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed

Your doctor may order this test if you have diabetes. It is used to measures your blood sugar control over several months. In general, the higher your HbA1c, the higher the risk that you will develop problems such as eye disease, kidney disease, nerve damage, heart disease, and stroke. This is especially true if your HbA1c remains high for a long period of time.

The closer your HbA1c is to normal, the less risk you have for these complications.

Normal Values

HbA1c is normal if it is 5% or less. Normal ranges may vary slightly depending on the laboratory used.

What abnormal results mean

Abnormal results mean that your blood glucose levels have not been well-regulated over a period of weeks to months. If your HbA1c is above 7%, it means your diabetes is poorly controlled.

High values mean you are at greater risk of diabetic complications. If you can bring your level down, you decrease your chances of long-term complications.

You should try to keep your level below 7%. Ask your doctor how often you should have your Hb A1c tested. Usually, doctors recommend testing every 3 or 6 months.

What the risks are

Risks related to getting your blood drawn include:

• Excessive bleeding
• Fainting or feeling lightheaded
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)
• Multiple punctures to locate veins

Special considerations

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

References

American Diabetes Association. Standards of medical care in diabetes—2007. Diabetes Care. 2007; 30(Suppl.1):S4-S41.

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