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

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.

No special preparation in necessary.

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.

Your doctor may order this test if you have diabetes. It is used to measures 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.

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.

An HbA1c of 6% or less is normal.

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

Abnormal results mean that your blood glucose levels have not been well-controlled 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.

In the past few years, doctors and diabetes experts have said you should try to keep your HbA1c level below 7%. However, researchers are finding that keeping the HbA1c below 7% may not be as helpful as they used to think.

Ask your doctor how often you should have your Hb A1c tested. Usually, doctors recommend testing every 3 or 6 months.

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)

American Diabetes Association. Standards of medical care in diabetes -- 2008. Diabetes Care. 2008;31:S12-S54.