What is the A1C test?

The A1C blood test, also called the hemoglobin A1C test, HbA1c, or glycohemoglobin test, reflects your average blood glucose levels for the past 3 months. Your health care provider will send you to a lab to have a small sample of your blood drawn for the test. Your health care provider might use the A1C test to diagnose your diabetes. After being diagnosed with diabetes, you should have the A1C test at least twice a year. Your health care provider uses the results of your A1C tests to see whether you need to make changes in your diabetes medicine, meal plan, or physical activity routine to keep your diabetes under control.

How do hemoglobin variants affect the A1C test and my diabetes care?

A variant form of hemoglobin in your blood can give you false A1C test results. If your test result is falsely high, your health care provider might think that you have diabetes when you don’t. Your health care provider might also change your diabetes medicine or make other changes in how you take care of your diabetes based on false A1C test results. These changes could cause low blood glucose, or hypoglycemia.

If your test result is falsely low, your health care provider might make changes in your treatment that could cause your blood glucose to stay too high, increasing your risk for diabetes problems in your eyes, nerves, and kidneys. Not all A1C tests are affected by variant hemoglobin. Your health care provider can take steps to make sure you get accurate results from your A1C test.

How will I know whether I have a hemoglobin variant?

Many people with hemoglobin variants have no health problems. You might be at risk for having a hemoglobin variant if

• you are of African, Mediterranean, or Southeast Asian heritage
• members of your family have sickle cell trait or sickle cell anemia
• the results of your blood glucose test or self-monitoring of blood glucose don’t match the results of your A1C test
• your A1C result is different than expected
• your A1C result is very high-above 15 percent
• your most recent A1C result is very different from your last A1C result

Your health care provider can order other blood tests to confirm whether you have a hemoglobin variant.

Where can my health care provider find more information about hemoglobin variants and the A1C test?

Your health care provider can access a fact sheet that explains the limitations of the A1C test online at www.diabetes.niddk.nih.gov or by calling the National Diabetes Information Clearinghouse at 1-800-860-8747.

How can I know if my diabetes is well controlled if I have a hemoglobin variant?

Some A1C tests give accurate results in people with a hemoglobin variant. Your health care provider can arrange for your A1C test to be done at a lab that gives accurate results for people with a hemoglobin variant. Your daily blood glucose tests can also show how well controlled your diabetes is, but keep in mind that each blood glucose test gives information for only one point in time.

Points to Remember

• If you are of African, Mediterranean, or Southeast Asian heritage, you are at risk for having a hemoglobin variant-a less common form of hemoglobin.
• You can have a hemoglobin variant but not know it.
• Having a hemoglobin variant does not increase your risk for diabetes, but it can affect your diabetes test results.
• A variant form of hemoglobin in your blood can give you false A1C test results. The results might show that your average blood glucose level is higher or lower than the actual level.
• Your health care provider can arrange for your A1C test to be done at a lab that gives accurate results for people with a hemoglobin variant.
• Your daily blood glucose tests can also show how well controlled your diabetes is, but keep in mind that each blood glucose test gives information for only one point in time.

Hope through Research

The NIDDK conducts and supports research related to the causes, treatment, and prevention of diabetes.

Participants in clinical trials can play a more active role in their own health care, gain access to new research treatments before they are widely available, and help others by contributing to medical research. For information about current studies, visit www.ClinicalTrials.gov.

Pronunciation Guide

glycohemoglobin (GLY-koh-HEE-moh-GLOH-bin)

hemoglobin (HEE-moh-GLOH-bin)

hemoglobin variants (HEE-moh-GLOH-bin) (VAIR-ee-uhnts)

hypoglycemia (HY-poh-gly-SEE-mee-uh)

sickle cell trait (SIH-kul) (sel) (trayt)

For More Information

American Diabetes Association
1701 North Beauregard Street
Alexandria, VA 22311
Phone: 1–800–DIABETES (1–800–342–2383)
Fax: 703–549–6995
Email: AskADA@diabetes.org
Internet: www.diabetes.org

For More Information about Sickle Cell Trait and Other Blood Conditions

National Heart, Lung, and Blood Institute Health Information Center
P.O. Box 30105
Bethesda, MD 20824–0105
Phone: 301–592–8573
Fax: 240–629–3246
Email: nhlbiinfo@nhlbi.nih.gov
Internet: www.nhlbi.nih.gov

Acknowledgments

Publications produced by the Clearinghouse are carefully reviewed by both NIDDK scientists and outside experts. This publication was originally reviewed by Randie R. Little, Ph.D., National Glycohemoglobin Standardization Program, University of Missouri School of Medicine.

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National Diabetes Education Program

1 Diabetes Way
Bethesda, MD 20814–9692
Phone: 1–888–693–NDEP (1–888–693–6337)
TTY: 1–866–569–1162
Fax: 703–738–4929
Email: ndep@mail.nih.gov
Internet: www.ndep.nih.gov
www.yourdiabetesinfo.org

The National Diabetes Education Program is a federally funded program sponsored by the U.S. Department of Health and Human Services’ National Institutes of Health and the Centers for Disease Control and Prevention and includes over 200 partners at the federal, state, and local levels, working together to reduce the morbidity and mortality associated with diabetes.

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National Diabetes Information Clearinghouse

1 Information Way
Bethesda, MD 20892-3560
Phone: 1-800-860-8747
TTY: 1-866-569-1162
Fax: 703-738-4929
Email: ndic@info.niddk.nih.gov
Internet: www.diabetes.niddk.nih.gov
The National Diabetes Information Clearinghouse (NDIC) is a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). The NIDDK is part of the National Institutes of Health of the U.S. Department of Health and Human Services. Established in 1978, the Clearinghouse provides information about diabetes to people with diabetes and to their families, health care professionals, and the public. The NDIC answers inquiries, develops and distributes publications, and works closely with professional and patient organizations and Government agencies to coordinate resources about diabetes.

This publication is not copyrighted. The Clearinghouse encourages users of this publication to duplicate and distribute as many copies as desired.

This publication may contain information about medications. When prepared, this publication included the most current information available. For updates or for questions about any medications, contact the U.S. Food and Drug Administration toll-free at 1-888-INFO-FDA (1-888-463-6332) or visit www.fda.gov. Consult your health care provider for more information.

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NIH Publication No. 12–6283
October 2011

Page last updated November 4, 2011