The Cleveland Clinic

Diabetes: The Glycated Hemoglobin Test (HbA1c)

The glycated hemoglobin test, (HbA1c, also called "hemoglobin A1c" or "glycohemoglobin" and sometimes incorrectly referred to as "glycosylated hemoglobin test") is an important blood test used to determine how well your diabetes is being controlled. The test provides an average of your blood glucose measurements over a six to 12 week period and is used in conjunction with home blood glucose monitoring to make adjustments in your diabetes medicines.

Hemoglobin is a substance within red blood cells that carries oxygen throughout your body. When your diabetes is not controlled (meaning that your blood glucose is too high), sugar builds up in your blood and combines with your hemoglobin, becoming "glycated." Therefore, the average amount of sugar in your blood can be determined by measuring an HbA1c. If your glucose levels have been high over recent weeks, your HbA1c test will be higher. The amount of HbA1c will reflect the last several weeks of blood glucoses, typically encompassing a period of 120 days.

For people without diabetes, the normal range for the HbA1c test is between 4% and 6%. Because studies have repeatedly shown that out-of-control diabetes results in complications from the disease, the goal for people with diabetes is an HbA1c less than 7%. The higher the HbA1c, the higher the risks of developing complications related to diabetes.

People with diabetes should have this test every three months to determine whether their blood sugars have reached the target level of control. Those who have their diabetes under good control may be able to wait longer between the blood tests, but experts recommend checking at least 2 times a year.

Patients with diseases affecting hemoglobin such as anemia may get abnormal results with this test. Other abnormalities that can affect the results of the HbA1c include supplements such as Vitamin C and E and high levels of lipids. Kidney disease and liver disease may also affect the result of the HbA1c test.

Reviewed by Certified Diabetes Educators in the Department of Patient Education and Health Information and by physicians in the Department of Endocrinology at The Cleveland Clinic.

Edited by Brunilda Nazario , MD, WebMD, October 2004.

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Last Editorial Review: 5/24/2005