Glycohemoglobin (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 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.
Why It Is Done
This test is done to:
Diagnose prediabetes and diabetes.
treatment for diabetes.
How To Prepare
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.
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
Attach a tube to the needle to fill it with blood.
Remove the band from your arm when enough blood is
Put a gauze pad or cotton ball over the needle site as the needle
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
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
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.
How this information was developed to help you make better health decisions.