Glycohemoglobin (HbA1c, A1c)
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.
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:
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:
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.
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.
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:
What To Think About
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