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HbA1c

Definition

HbA1c is a test that measures the amount of glycated hemoglobin in your blood. Glycated hemoglobin is a substance in red blood cells that is formed when blood sugar (glucose) attaches to hemoglobin.

Alternative Names

Glycated hemoglobin; 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 germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

How to Prepare for the Test

No special preparation is 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 measure your blood sugar control over several months. It can give a good estimate of how well you have managed your diabetes over the last 2 or 3 months.

The test may also be used to screen for diabetes.

You have more glycated hemoglobin if you have had high levels of glucose in your blood. In general, the higher your HbA1c, the higher the risk that you will develop problems such as:

  • Eye disease
  • Heart disease
  • Kidney disease
  • Nerve damage
  • 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 Results

An HbA1c of 6% or less is normal. A HbA1c above 6.5% is a newly recommended criterion for diagnosing diabetes.

If you have diabetes, you should try to keep your HbA1c level at or below 7%. However, you and your health care provider must decide what is a normal HbA1c level for you.

Normal ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What Abnormal Results Mean

Abnormal results mean that your blood glucose levels have been above normal over a period of weeks to months. If your HbA1c is above 7%, it means that your diabetes control may not be as good as it should be.

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

Ask your doctor how often you should have your HbA1c tested. Usually, doctors recommend testing every 3 or 6 months.

Risks

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.

Other risks associated with having blood drawn are slight but may include:

  • Excessive bleeding
  • Fainting or feeling light-headed
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)

References

International Expert Committee Report on the Role of the A1C Assay in the Diagnosis of Diabetes. Diabetes Care. July 2009 32:1344-1345.

American Diabetes Association. Standards of medical care in diabetes--2010. Diabetes Care. 2010 Jan;33 Suppl 1:S11-61.


Review Date: 4/19/2010
Reviewed By: Ari S. Eckman, MD, Division of Endocrinology and Metabolism, Johns Hopkins School of Medicine, Baltimore, MD. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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