Glycosylated Hemoglobin Test
(HbA1c; GHb; Glycohemoglobin; Diabetic Control Index)En Español (Spanish Version)
Glycosylated hemoglobin test (HbA1c) is a blood test that measures the amount of glycosylated hemoglobin (hemoglobin that is chemically linked to glucose) in the blood.
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Reasons for Procedure
People with untreated or poorly controlled diabetes are at risk for complications that include damage to the eyes, kidneys, heart, nerves, feet, and blood vessels. There is good evidence that controlling diabetes to a HbA1c level of less than 7% will decrease complications related to the kidneys, eyes, and nerves.
HbA1c indicates how close to normal your blood sugar levels have been during the past three months. More specifically, the test is an unevenly weighted average of your past three months blood sugar, with the levels in the most recent two weeks influencing the result most heavily. This information, along with the results of your self-glucose monitoring, can help your doctor determine how well you are responding to treatment, or if your treatment needs to be changed.
If you have been newly diagnosed with diabetes, or you are pregnant and have diabetes, your doctor may order this test more frequently (perhaps once a week or once a month) until your sugars have stabilized. Currently, there are no well-controlled studies available to support a definite testing schedule. According to the American Diabetes Association, expert opinion recommends testing at least twice a year in people who have “good” control of their diabetes (HbA1c level of less than 7%), and four times a year in people who lack good control, or whose treatment regimens have changed. Talk with your doctor about how frequently you should be tested.
Risk Factors for Complications During the Procedure
Collecting blood from a vein carries minimal risk. Some people may develop a bruise, or a small collection of blood under the skin at the site of the needlestick, called a hematoma. The chance of a hematoma developing is greater for people taking aspirin or other blood-thinning medications (ie, Coumadin or Plavix ).
What to Expect
Prior to Procedure
Carry on as you would any other day, there is no need to fast.
A blood sample is taken from a vein, usually from the inside of your elbow or the back of your hand.
There is no anesthesia necessary for this procedure.
To reduce bruising, apply pressure to the puncture site until bleeding stops.
Description of the Procedure
You roll up your sleeve, if necessary, and the puncture site (usually a vein from the inside of the arm or back of the hand) is cleaned with antiseptic. A tourniquet (elastic band) is tied around the upper arm, causing the vein to fill with blood. A needle is inserted into the vein, and blood is collected in an airtight vial or syringe. The tourniquet is untied, the needle is removed, and the puncture site is covered to stop any bleeding. The blood sample is then sent to the laboratory for testing.
How Long Will It Take?
Drawing the blood sample should take less than five minutes. Laboratory results are usually available within one week.
Will It Hurt?
You may feel a prick of pain as the needle is inserted into your vein.
- Excessive bleeding
- Fainting (rare) or feeling lightheaded
- Bruising (small amount of blood collecting under the skin)
- Hematoma (larger amount of blood accumulating under the skin)
- Infection (this is rare)
- Multiple punctures to locate vein
Average Hospital Stay
None. This test is performed in your doctor's office or in a clinic or hospital laboratory.
The glycosylated hemoglobin goal for a person being treated for diabetes is less than 7%. Since the evidence points to a continued decrease in complications the closer a person gets to normal, your doctor may set a lower goal for you, to near normal or about 6%. The American Association of Clinical Endocrinologists and the American College of Endocrinology have set a goal of less than 6.5%. Talk to your doctor about what goal is right for you. If your HbA1c levels are high, you probably need a change in treatment. This may involve changing your diabetes medications, increasing your level of physical activity, and/or modifying your diet.
For people without diabetes, normal HbA1c values range from 4%-6%. Although efforts have been made to standardize this test, some labs may use different techniques. Be sure to check what the normal range is for your lab, and if you change labs be aware that this could be a factor.
American Diabetes Association
National Diabetes Education Program
BC Health Guide
Canadian Diebetes Association
A1c test. American Diabetes Association website. Available at: http://www.diabetes.org/main/type1/medical/blood_sugar/glyc_hemoglobin.jsp?WTLPromo=SEARCH_a1ctest . Accessed April 1, 2003.
Check your hemoglobin A1c I.Q. National Diabetes Education Program website. Available at: http://ndep.nih.gov/materials/pubs/HbA1c/HbA1c-checkIQ.htm . Accessed April 1, 2003.
Glycosylated hemoglobin. MedlinePlus Health Information. National Library of Medicine and the National Institutes of Health website. Available at: http://www.nlm.nih.gov/medlineplus/ency/article/003640.htm . Accessed March 26, 2003.
Why is interpreting Hb/a1c values tricky? Available at: http://www.faqs.org/faqs/diabetes/faq/part2/preamble.html. Accessed April 13, 2003.
Last reviewed February 2008 by Ronald Nath, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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