Glycohemoglobin (HbA1c, A1c)
Glycohemoglobin is a blood test that checks the amount of sugar (glucose) bound to hemoglobin. Normally, only a small percentage of hemoglobin in the blood (4% to 6%) has glucose bound to it. People who have diabetes or other conditions that increase their blood glucose levels have more glycohemoglobin than normal.
The glycohemoglobin A1c can be used to diagnose diabetes. The glycohemoglobin A1c test checks the long-term control of blood glucose levels in people with diabetes. Most doctors think the glycohemoglobin 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 because of 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 glycohemoglobin test is one blood sample every 3 to 4 months, and the test 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 medicine needs to be changed.
The A1c level 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. The lower your A1c level, the 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 a glycohemoglobin 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.
Glycohemoglobin 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 A1c level may be reported without a total glycohemoglobin value. Your doctor will have your test results in 1 to 2 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.
The ADA recommends that adults with diabetes have an A1c level less than 7%. If your A1c level is higher than 7%, you may need changes in your diabetes treatment.2 Talk to your doctor about your diabetes treatment plan and goals.
A glycohemoglobin A1c level higher than the level that is listed in the table above means that your diabetes has been poorly controlled over the last 2 to 3 months.
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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