Glycosylated Hemoglobin Test (A1c)
What’s a glycosylated hemoglobin test?
A glycosylated hemoglobin test measures the amount of glucose (sugar) in your blood. The test is often called A1c, or sometimes HbA1c. It’s a simple blood test used to:
- Detect prediabetes — high sugar levels that can lead to diabetes, heart disease and stroke.
- Diagnose diabetes.
- Tell how well a person with diabetes has been managing the disease.
How does the A1c test work?
A1c testing relies on hemoglobin. Hemoglobin is the part of the red blood cell that carries oxygen throughout the body. When you have glucose in your blood, it glycates (sticks) to hemoglobin. The more glucose in your blood, the more it sticks. And it can stay there for around three months, or about how long the average red blood cell lives.
The A1c test measures the average amount of glucose that’s been attached to hemoglobin over time. So the A1c test provides more information about blood sugar over a longer period of time than home monitoring does.
When is an A1c test needed?
If you have diabetes, you should have an A1c test two to four times a year to see how you’re managing it. Your healthcare team will recommend exactly how often you should get tested.
If you haven’t gotten diagnosed with diabetes, a healthcare provider may order an A1c test if you have symptoms of the condition. These symptoms include:
- Blurry vision.
- Fatigue, or feeling tired all the time.
- Increased urination (peeing).
- Unusual thirst.
You may also get an A1c test if you’re at risk for diabetes. Risk factors include:
How do I prepare for an A1c test?
You don’t need to fast (restrict food or drink) or do anything else special before the test.
What happens during an A1c test?
Some healthcare provider offices have an A1c machine that requires only a small drop of blood from the fingertip (similar to a home glucose check) and provides a result in just a few minutes.
Other healthcare providers may order the A1c as a lab test to be drawn in the medical office, a hospital or a lab. The test usually takes less than five minutes, and it often takes a day or two to get the result.
The person drawing your blood will:
- Ask you to expose your upper arm (for example, by rolling up your sleeve).
- Put a tight band called a tourniquet around your upper arm.
- Clean the area on the inner arm, where it bends.
- Insert a thin needle into a vein.
- Collect blood into a tube attached to the needle.
- Remove the needle, then put a bandage on the tiny hole.
Are there any risks with an A1c test?
Blood tests are very common and don’t carry any significant risks. You may have slight pain when the needle gets inserted, and a small bruise may develop there.
Results and Follow-Up
When will I know the results of the A1c test?
Ask your healthcare provider when you can expect to get the results. They may be ready the same day or up to a week later.
What do the A1c test results mean?
An A1c test result gets reported as a percentage. The number represents the portion of hemoglobin proteins that are glycosylated, or holding glucose. The higher the percentage, the higher your blood sugar levels have been over the last few months.
- Less than 5.7% means you don’t have diabetes.
- 5.7% to 6.4% signals pre-diabetes.
- 6.5% or higher means a diabetes diagnosis.
- 7% or lower is the goal for someone trying to manage their diabetes.
What is A1c compared to eAg?
If you have diabetes and track glucose with a home monitor, your healthcare provider might report A1C results as eAG. This converts the information to a different way of measuring. You can then compare it to the results of home glucose monitoring.
Instead of a percentage, eAG gets reported in milligrams per deciliter (mg/dl) or millimoles per liter (mmol/l). For example, an A1c level of 7% equals an eAG of 154 mg/dl and 8.6 mmol/l. The American Diabetes Association offers a calculator and chart to help you convert your numbers.
Can my race or ethnicity affect my A1c results?
There are different kinds of hemoglobin. The most common is hemoglobin A. But some races and ethnicities have different types of hemoglobin, called hemoglobin variants.
A hemoglobin variant doesn’t increase the risk for diabetes, but it can affect A1c results. Labs have different ways to do A1c tests on blood with a hemoglobin variant.
The most common variants are the:
- Hemoglobin C trait that’s most commonly found in African Americans, people of West African descent and people from South and Central America, the Caribbean Islands and Europe.
- Hemoglobin D trait that’s most commonly found in people who live in China, India, Turkey, Brazil and some parts of Europe.
- Hemoglobin E trait that’s most commonly found in Asian Americans, especially those of Southeast Asian descent.
- Hemoglobin S trait that’s most commonly found in African Americans and Latino Americans.
Talk to your healthcare provider about how often you should get an A1c test. Also discuss whether you might have a hemoglobin variant that could affect the results.