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 treatment plan is working. 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 managed in the last 2 to 3 months and whether your diabetes treatment plan needs to be changed. This test may not be accurate for everyone because many things can affect the life span of red blood cells, such as the second or third trimester of pregnancy, a recent blood loss or a blood transfusion, sickle cell disease, hemodialysis, or erythropoietin (ESA) medicine.
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
The A1c test is one of the tests used to diagnose prediabetes and diabetes. If you have diabetes, this test is done to check how well your diabetes has been managed over the past 2 to 3 months. Your doctor can use this information to adjust your treatment, if needed.
How To Prepare
You don't need to stop eating before you have an A1c test. This test can be done at any time during the day, even after a meal.
How It Is Done
A health professional uses a needle to take a blood sample, usually from an arm. It can also be done using blood from a finger stick.
How It Feels
You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little chance of having a problem from this test. A small bruise may form at the site.
Current as of: April 13, 2022
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