Hemoglobin A1C (HbA1c) Test

A hemoglobin A1C (HbA1C) test is a blood test that shows your average level of blood glucose, also called blood sugar, over the past two to three months. Glucose is a type of sugar in your blood that comes from the foods you eat. Your cells use glucose for energy.

A hormone called insulin helps glucose get into your cells. If you have diabetes your body doesn't make enough insulin, or your cells don't use it well. As a result, glucose can't get into your cells, so your blood glucose levels increase.

Glucose in your blood sticks to hemoglobin, a protein in your red blood cells. As your blood glucose levels increase, more of your hemoglobin will be coated with glucose. An A1C test measures the percentage of your red blood cells that have glucose-coated hemoglobin.

An A1C test can show your average glucose level for the past three months because: Glucose sticks to hemoglobin for as long as the red blood cells are alive.; Red blood cells live about three months.; High A1C levels are a sign of high blood glucose from diabetes. Diabetes can cause serious health problems, including heart disease, kidney disease, and nerve damage. But with treatment and lifestyle changes, you can control your blood glucose levels.

Why this test is done

The Centers for Disease Control (CDC) recommends A1C testing for diabetes and prediabetes if:

• You are over age 45.
• If your results are normal, your provider will tell you how often you should be tested based on your age and risk factors.
• If your results show you have prediabetes, you will usually need to be tested every 1 to 2 years. Ask your provider how often to get tested and what you can do to reduce your risk of developing diabetes.
• If your results show you have diabetes, you should get an A1C test at least twice a year to monitor your condition and treatment.
• You are under 45 and are more likely to develop diabetes because you:
• Have prediabetes.
• Are overweight or have obesity.
• Have a parent or sibling with type 2 diabetes.
• Have high blood pressure or high cholesterol levels.
• Have heart disease or have had a stroke.
• Are physically active less than 3 times a week.
• Have had gestational diabetes (diabetes during pregnancy) or given birth to a baby over 9 pounds.
• Are African American, Hispanic or Latino, American Indian, or an Alaska Native person. Some Pacific Islander and Asian American people also have a higher risk of developing diabetes.
• Have polycystic ovarian syndrome (PCOS).

You may also need an A1C test if you have symptoms of diabetes, such as:

• Feeling very thirsty
• Urinating (peeing) a lot
• Losing weight without trying
• Feeling very hungry
• Blurred vision
• Numb or tingling hands or feet
• Fatigue
• Dry skin
• Sores that heal slowly
• Having more infections than usual

How to prepare

Certain medicines such as opioids and some HIV medicines may affect your results, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to. Also, let your health care provider know if you are pregnant, since this may affect your results.

Sample type

Blood

Other names for this test

HbA1C, A1C, glycohemoglobin, glycated hemoglobin, glycosylated hemoglobin