A1C test

The A1C test is a common blood test for people who have type 1 or type 2 diabetes. The A1C test also goes by many other names, including glycated hemoglobin, glycosylated hemoglobin, hemoglobin A1C and HbA1c.

Unlike finger sticks you can do at home, which measure your blood sugar level at a given time, the A1C test reflects your average blood sugar level for the past two to three months. The A1C test doesn’t tell you what’s happening at the moment. Instead, it helps your doctor gauge how well you’re managing your diabetes overall.

Specifically, the A1C test measures what percentage of your hemoglobin — a protein in red blood cells that carries oxygen — is coated with sugar (glycated). The higher your A1C level, the poorer your blood sugar control and the higher your risk of diabetes complications.

The A1C test measures your average blood sugar level for the past two to three months. Unlike daily blood sugar monitoring, which only measures your blood sugar level at a point in time, the A1C test indicates how well your diabetes treatment plan is working overall.

Your doctor may recommend the A1C test when you’re first diagnosed with diabetes to establish a baseline and to determine your blood sugar level for the past few months. The A1C test may need to be repeated while you’re learning to control your blood sugar.

Later, how often you need the A1C test depends on the type of diabetes you have and how well you’re managing your blood sugar. For example, the A1C test may be recommended:

  • Twice a year if you have type 2 diabetes, you don’t use insulin, and your blood sugar level is consistently within your target range
  • Three to four times a year if you have type 1 diabetes
  • Four times a year if you have type 2 diabetes, you use insulin to manage your diabetes, or you 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.

During the A1C test, a member of your health care team simply takes a sample of blood by pricking your fingertip or inserting a needle into a vein in your arm. The blood sample is sent to a lab for analysis. You can return to your usual activities immediately.

For someone who doesn’t have diabetes, a normal A1C level is about 5 percent — although it can range from 4.5 to 6 percent. Someone who’s had uncontrolled diabetes for a long time might have an A1C level as high as 25 percent.

For most people who have diabetes, an A1C level of 7 percent or less is a common target. If your A1C level is higher than 7 percent, your doctor may recommend a change in your diabetes treatment plan. Remember, the higher your A1C level, the higher your risk of diabetes complications.

Here’s how A1C level corresponds to average blood sugar level, in milligrams per deciliter (mg/dL) and millimoles per liter (mmol/L):

A1C level Average blood sugar level
5 percent 80 mg/dL (4.4 mmol/L)
6 percent 120 mg/dL (6.7 mmol/L)
7 percent 150 mg/dL (8.3 mmol/L)
8 percent 180 mg/dL (10 mmol/L)
9 percent 210 mg/dL (11.7 mmol/L)
10 percent 240 mg/dL (13.3 mmol/L)
11 percent 270 mg/dL (15 mmol/L)
12 percent 300 mg/dL (16.7 mmol/L)
13 percent 333 mg/dL (18.5 mmol/L)
14 percent 360 mg/dL (20 mmol/L)

It’s important to note that the effectiveness of A1C tests may be limited in certain cases. For example:

  • If you experience heavy or chronic bleeding, your hemoglobin stores may be depleted. This may make your A1C test results falsely low.
  • If you don’t have enough iron in your bloodstream, your A1C test results may be falsely high.
  • Most people have only one type of hemoglobin, called hemoglobin A. If you have an uncommon form of hemoglobin (known as a hemoglobin variant), your A1C test result may be falsely high or falsely low. Hemoglobin variants are most likely in blacks and people of Mediterranean or Southeast Asian heritage. Hemoglobin variants can be confirmed with lab tests. If you’re diagnosed with a hemoglobin variant, your A1C tests may need to be done at a specialized lab for the most accurate results.

Also keep in mind that the normal range for A1C results may vary somewhat among labs. If you consult a new doctor or use a different lab, it’s important to consider this possible variation when interpreting your A1C test results.