As shown in the figure below, hemoglobin can also exist in a glycosylated form known as HbA1C. HbA1C is formed when the amino terminus of HbA reacts with glucose, first reversibly forming an aldimin or Schiff's Base, and then undergoing an irreversible Amadori rearrangement to afford the ketamine form HbA1C. In normal patients, HbA1C accounts for about 3-5% of HbA, but in diabetics who have elevated blood glucose for extended periods, this number can reach 6 to 15%. Physicians can measure HbA1C, and are using it as a reliable way to monitor how well diabetic patients are complying with their insulin therapy.

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Glycohemoglobin is a blood test that checks the amount of sugar (glucose) bound to hemoglobin. Normally, only a small percentage of hemoglobin in the blood (4% to 6%) has glucose bound to it. People who have diabetes or other conditions that increase their blood glucose levels have more glycohemoglobin than normal.

The glycohemoglobin A_1c test checks the long-term control of blood glucose levels in people with diabetes. Most doctors think the glycohemoglobin A_1c level is the best way to check how well a person is controlling his or her diabetes.

A home blood glucose test measures the level of blood glucose only at that moment. Blood glucose levels change during the day because of diet, exercise, and the level of insulin in the blood.

It is useful for a diabetic to have information about the long-term control of blood sugar levels. The glycohemoglobin test is one blood sample every 3 to 4 months, and the test does not change with any recent changes in diet, exercise, or medicines.

Glucose binds to hemoglobin in red blood cells at a steady rate. Since red blood cells last 3 to 4 months, the glycohemoglobin A_1c test shows how much glucose is in the plasma part of blood. This test shows how well your diabetes has been controlled in the last 2 to 3 months and whether your diabetes medicine needs to be changed.

The A_1c level can also help your doctor see how big your risk is of developing problems from diabetes, such as kidney failure, vision problems, and leg or foot numbness. The lower your A_1c level, the lower your chance for problems.

Glycohemoglobin is a blood test that checks the amount of sugar (glucose) bound to hemoglobin. The result is shown as a percentage and may be compared with a number value. Your A_1c level may be reported without a total glycohemoglobin value. Your doctor will have your test results in 1 to 2 days.

Normal

Normal values vary from lab to lab, depending on the test method used.

The American Diabetes Association (ADA) recommends that people with diabetes have an A_1c level less than 7%. If levels are greater than 8%, the ADA recommends that diabetes treatment be looked at and changed as needed.

High values

A glycohemoglobin A_1c level above 8% means that your diabetes has been poorly controlled over the last 2 to 3 months.

Some medical conditions can increase A_1c levels, but the results may still be within a normal range. These conditions include Cushing's syndrome, pheochromocytoma, and polycystic ovary syndrome (PCOS).

Corticosteroid treatment increases the A_1c level.

A_1c levels may be higher in pregnant women.

What To Think About

• If you have diabetes, your doctor may recommend that you have a glycohemoglobin test every 3 to 6 months, depending on your type of diabetes and how well it is controlled. For most people, A_1c is measured 3 to 4 times a year.
• The glycohemoglobin test does not replace the need for other regular blood glucose tests, including checking your blood sugar at home and a regular blood glucose test. For more information, see the medical test Home Blood Glucose Test and Blood Glucose.
• Many people with diabetes have high blood sugars at times when they would not be checking their blood sugar, such as after meals or during the night. Glycohemoglobin A_1c may show these periods of high blood sugar that would not be found by a home blood glucose test.
• Some people who develop diabetes have normal glycohemoglobin tests early in the course of their disease.
• Glycohemoglobin levels can be normal in some people who have untreated diabetes and certain medical conditions, such as sickle cell anemia, hemolytic anemia, severe kidney disease, or pregnancy.
• If you have diabetes, having a high glycohemoglobin level increases your chances of having other problems. Lowering your glycohemoglobin levels can help delay or prevent problems, such as serious nerve, kidney, and eye damage.
• Glycohemoglobin levels are not useful for finding low blood sugar (hypoglycemia).

© 1995-2006, Healthwise, Incorporated, P.O. Box 1989, Boise, ID 83701. ALL RIGHTS RESERVED.

This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information. For more information, please read the Healthwise Terms and Conditions. How this information was developed.