Glycohemoglobin (HbA1c, A1c)

Test Overview

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 A1c is used to diagnose diabetes. The glycohemoglobin A1c test checks the long-term control of blood glucose levels in people with diabetes. Most doctors think the glycohemoglobin A1c 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 A1c 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 A1c 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 A1c level, the lower your chance for problems.

Why It Is Done

This test is done to:

  • Diagnose diabetes.
  • Check your treatment for diabetes.

How To Prepare

You do not need to stop eating before you have a glycohemoglobin test. This test can be done any time during the day, even after a meal.

How It Is Done

The health professional taking a sample of your blood will:

  • Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
  • Clean the needle site with alcohol.
  • Put the needle into the vein. More than one needle stick may be needed.
  • Attach a tube to the needle to fill it with blood.
  • Remove the band from your arm when enough blood is collected.
  • Put a gauze pad or cotton ball over the needle site as the needle is removed.
  • Put pressure on the site and then put on a bandage.

How It Feels

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

Risks

Blood test

There is very little chance of a problem from having blood sample taken from a vein.

  • You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
  • In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
  • Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Results

Glycohemoglobin is a blood test that checks the amount of sugar (glucose) bound to hemoglobin. The result is shown as a percentage. The result of your A1c test can also be used to estimate your average blood sugar level. This is called your estimated average glucose, or eAG. Your A1c 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.

Glycohemoglobin (GHb)
Glycohemoglobin A1c:

4.5%–5.7%

Total glycohemoglobin:

5.3%–7.5%

The American Diabetes Association (ADA) recommends that people with diabetes have an A1c level less than 7%. If your A1c level is higher than 7%, you may need changes in your diabetes treatment.1 Talk to your doctor about your diabetes treatment plan and goals.
A1c and estimated average glucose (eAG) 2
A1c % Estimated average plasma glucose (mg/dL) Estimated average plasma glucose (mmol/L)
6%

126

7.0

7%

154

8.6

8%

183

10.2

9%

212

11.8

10%

240

13.4

11%

269

14.9

12%

298

16.5

The American Diabetes Association has the following recommendations for children and adolescents with diabetes:3

A1c recommendations for children and teens
Age A1c %
Children younger than 6 years old 7.5–8.5%
Children ages 6–12 years old Less than 8%
Teens ages 13–19 years old Less than 7.5%

High values

A glycohemoglobin A1c level above 8% means that your diabetes has been poorly controlled over the last 2 to 3 months.

Some medical conditions can increase A1c 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 A1c level.

A1c levels may be higher in children and adolescents with diabetes.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • Having severe blood loss or a blood transfusion in the last 3 months.
  • Having certain medical conditions, such as sickle cell anemia, hemolytic anemia, some types of thalassemia, and severe kidney disease.
  • Having your spleen taken out. This changes the normal life cycle of red blood cells and A1c levels.

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, A1c 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 A1c 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).

References

Citations

  1. American Diabetes Association (2009). Medical management of hyperglycemia in type 2 diabetes: A consensus algorithm for the initiation and adjustment of therapy. Diabetes Care, 32: 193–203.
  2. Nathan DM, et al. (2008). Translating the A1c assay into estimated average glucose values. Diabetes Care, 31(8): 1473–1478.
  3. American Diabetes Association (2005). Care of children and adolescents with type 1 diabetes. Diabetes Care, 28(1): 186–212.

Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
  • Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.

Credits

Author Caroline Rea, RN, BS, MS
Editor Maria Essig
Associate Editor Tracy Landauer
Primary Medical Reviewer Martin Gabica, MD - Family Medicine
Specialist Medical Reviewer David C.W. Lau, MD, PhD, FRCPC - Endocrinology & Metabolism
Last Updated May 29, 2008

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