The A1C test is a common blood test used to diagnose type 1 and type 2 diabetes. If you're living with diabetes, the test is also used to monitor how well you're managing blood sugar levels. The A1C test is also called the glycated hemoglobin, glycosylated hemoglobin, hemoglobin A1C or HbA1c test.

An A1C test result reflects your average blood sugar level for the past two to three months. Specifically, the A1C test measures what percentage of hemoglobin proteins in your blood are coated with sugar (glycated). Hemoglobin proteins in red blood cells transport oxygen.

The higher your A1C level is, the poorer your blood sugar control and the higher your risk of diabetes complications.

The results of an A1C test can help your doctor or other health care provider:

• Diagnose prediabetes. If you have prediabetes, you have a higher risk of developing diabetes and cardiovascular disease.
• Diagnose type 1 and type 2 diabetes. To confirm a diabetes diagnosis, your doctor will likely look at the results of two blood tests given on different days — either two A1C tests or the A1C test plus another test, such as a fasting or random blood sugar test.
• Monitor your diabetes treatment plan. The result of an initial A1C test also helps establish your baseline A1C level. The test is then repeated regularly to monitor your diabetes treatment plan.

How often you need the A1C test depends on the type of diabetes, your treatment plan, how well you're meeting treatment goals and your primary care doctor's clinical judgment. For example, the A1C test may be recommended:

• Once every year if you have prediabetes
• Twice a year if you don't use insulin and your blood sugar level is consistently within your target range
• Four times a year if you take insulin or have trouble keeping your blood sugar level within your target range

You may need more-frequent A1C tests if your doctor changes your diabetes treatment plan or you begin taking a new diabetes medication.

The A1C test is a simple blood test. You don't need to fast for the A1C test, so you can eat and drink normally before the test.

During the A1C test, a member of your health care team takes a blood sample by inserting a needle into a vein in your arm or pricking your finger tip with a small, pointed lancet. If the blood is taken from a vein, the blood sample is sent to a lab for analysis.

Blood from a finger prick may be analyzed in your doctor's office for same-day results. This in-office test is only used for monitoring your treatment plan, not for diagnosis or screening.

A1C test results are reported as a percentage. A higher A1C percentage corresponds to higher average blood sugar levels. Results for a diagnosis are interpreted as follows:

• Below 5.7% is normal.
• 5.7% to 6.4% is diagnosed as prediabetes.
• 6.5% or higher on two separate tests indicates diabetes.

For most adults living with diabetes, an A1C level of less than 7% is a common treatment target. Lower or higher targets may be appropriate for some people.

The target of less than 7% is associated with a lower risk of diabetes-related complications. If your A1C level is above your target, your doctor may recommend an adjustment in your diabetes treatment plan.

A1C and self-monitoring

A part of your treatment plan will include self-monitoring at home with a blood glucose meter or other device. Your health care team will direct you on how often and when you should test your blood sugar.

Your self-monitoring device reports your blood sugar levels in milligrams of sugar per deciliter (mg/dL) or millimoles of sugar per liter (mmol/L). The measurement shows your blood sugar level at the time you do the test. Therefore, there is some variability throughout the day based on eating, exercise, stress and other factors.

Self-monitoring helps you make choices about diet and exercise and daily treatment goals, but it also helps you track whether you are meeting your A1C target. For example, if your A1C target is below 7%, your self-monitoring blood sugar levels should be, on average, below 154 mg/dL (8.6 mmol/L).

A1C test results generally correspond with the following results of blood sugar levels:

Limitations of the A1C test

Some factors may interfere with the accuracy of A1C test results. These include:

• Pregnancy
• Recent or heavy blood loss
• Recent blood transfusion
• Conditions that result in insufficient red blood cells (anemias)
• Hemoglobin variants

The most common form of the oxygen-transporting hemoglobin protein is called hemoglobin A. The presence of other variants of the protein may result in inaccurate A1C test results. Hemoglobin variants are more common among people of African, Mediterranean or Southeast Asian descent.

If you have a hemoglobin variant, your test may need to be sent to a specialized lab or you may need a different test for diagnosis and monitoring of diabetes.