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. 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. This test can be done with a blood draw from a vein. Sometimes an A1c test can be done with blood from a finger stick.
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.
It is 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 medicines.
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.
- Check your 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 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.
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.
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 criteria from Diabetes Canada used to diagnose diabetes includes the option of testing A1c. Your doctor may repeat the test to confirm the diagnosis of diabetes.
Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.
Less than 6.0%
Prediabetes (increased risk for diabetes)
6.5% and higher
If you have diabetes, talk to your doctor about your diabetes treatment plan and your target A1c goal.
Estimated average plasma glucose ( mmol/L)
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.
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.
- Being on hemodialysis.
- Taking erythropoietin (ESA) medicine.
- Being in the second or third trimester of pregnancy.
- Having your spleen taken out. This changes the normal life cycle of red blood cells and A1c levels.
- Diabetes Canada Clinical Practice Guidelines Expert Committee, et al. (2018). Definition, classification and diagnosis of diabetes, prediabetes and metabolic syndrome. Canadian Journal of Diabetes, 42(Suppl 1): S10–S15. DOI: 10.1016/j.jcjd.2017.10.003. Accessed October 15, 2018.
- American Diabetes Association (2019). Standards of medical care in diabetes—2019. Diabetes Care, 42(Suppl 1): S1–S193. Accessed December 17, 2018.
Current as of: December 20, 2019
Author: Healthwise Staff
E. Gregory Thompson MD - Internal Medicine
Kathleen Romito MD - Family Medicine
Adam Husney MD - Family Medicine
Matthew I. Kim MD - Endocrinology
David C.W. Lau MD, PhD, FRCPC - Endocrinology
Current as of: December 20, 2019