Home > Health Library > Glycohemoglobin (HbA1c, A1c)
A glycohemoglobin test, or hemoglobin A1c, is a blood test that checks the amount of sugar
(glucose) bound to
the hemoglobin in the red blood cells. When hemoglobin and glucose bond, a coat of sugar forms on the hemoglobin. That coat gets thicker when there's more sugar in the blood. A1c tests measure how thick that coat has been over the past 3 months, which is how long a red blood cell lives. People who have
diabetes or other conditions that increase their blood
glucose levels have more glycohemoglobin (sugar bound to hemoglobin) than normal.
An A1c test can be used to diagnose prediabetes or diabetes. The
A1c test checks the long-term control of blood glucose levels
in people with diabetes. Most doctors think checking an 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 for many reasons, including medicine, diet, exercise, and the level of insulin in the blood.
useful for a person who has diabetes to have information about the long-term control of blood
sugar levels. The A1c test result does not change with any recent changes in diet, exercise, or
Glucose binds to hemoglobin in red blood cells at a
steady rate. Since red blood cells last 3 to 4 months, the 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 treatment plan needs to be changed.
The A1c test 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. Keeping your A1c level in your target range can lower your chance for problems.
This test is done to:
You do not need to stop eating before
you have an A1c test. This test can be done any time during the day,
even after a meal.
The health professional taking a sample
of your blood will:
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
There is very little chance of a
problem from having blood sample taken from a vein.
A1c 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 doctor will have your test results in a few days.
The American Diabetes Association (ADA) criteria to diagnose diabetes includes the option of testing A1c. The diagnosis of diabetes needs to be confirmed by repeating the same blood sugar test or doing a different test on another day.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Less than 5.7%
6.5% and higher
The ADA recommends that most nonpregnant adults who have type 1 or type 2 diabetes have an A1c level less than 7%.2 The American Academy of Pediatrics recommends that most children with type 2 diabetes have an A1c level less than 7%.3 Talk to your doctor about your diabetes treatment plan and your target A1c goal.
Some medical conditions can increase A1c levels, but the
results may still be within a normal range. These conditions include
polycystic ovary syndrome (PCOS).
Corticosteroid treatment increases the A1c
Reasons you may not be able to
have the test or why the results may not be helpful include:
American Diabetes Association (2012). Diagnosis and classification of diabetes mellitus. Diabetes Care, 35(Suppl 1): S64–S71.
American Diabetes Association (2014). Standards of medical care in diabetes—2014. Diabetes Care, 37(Suppl 1): S14–S80. DOI: 10.2337/dc14-S014. Accessed January 7, 2014.
American Academy of Pediatrics (2013). Clinical Practice Guideline: Management of newly diagnosed type 2 diabetes mellitus (T2DM) in children and adolescents. Pediatrics, 131(2): 364–382. Also available online: http://pediatrics.aappublications.org/content/131/2/364.full.html.
Other Works Consulted
Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
Current as of:
June 4, 2014
E. Gregory Thompson, MD - Internal Medicine & David C.W. Lau, MD, PhD, FRCPC - Endocrinology
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