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.
Portions of this page copyright © The Cleveland Clinic
2000-2005
Last Editorial Review: 5/24/2005
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