A1C levels: what the numbers mean

What the A1C test measures

The A1C test is a blood test that shows your average blood glucose (blood sugar) over the past 3 months. It is also called hemoglobin A1C, HbA1c, glycated hemoglobin or glycohemoglobin. Glucose attaches to hemoglobin in red blood cells, and the higher your blood glucose, the more glucose attaches. The result is a percentage: the higher the percentage, the higher your blood glucose has been (NIDDK).

The test can be used to diagnose type 2 diabetes and prediabetes, and it is the main test used to manage diabetes. You do not have to fast before it (NIDDK). MedlinePlus notes that it is different from the blood sugar checks people with diabetes do every day (MedlinePlus).

A1C ranges

These are the ranges as printed by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) (NIDDK):

NIDDK adds that any test used to diagnose diabetes needs a second measurement to confirm it, unless there are clear symptoms of diabetes. If you have no symptoms but the A1C shows diabetes or prediabetes, the test should be repeated on a different day (NIDDK). MedlinePlus gives the same normal and prediabetes ranges and words the diabetes range as "above 6.5%" (MedlinePlus); the table above uses the NIDDK wording, which includes 6.5.

Within the prediabetes range of 5.7 to 6.4 percent, the higher the A1C, the greater the risk of diabetes (NIDDK). MedlinePlus says people with prediabetes may need a retest every year (MedlinePlus). More on what to do next is on the prediabetes page.

How the test is used for diagnosis

• For diagnosis, the blood is drawn from a vein and sent to a lab that uses an NGSP-certified method. NIDDK says point-of-care tests done in a doctor's office or clinic should not be used for diagnosis (NIDDK).
• The A1C test should not be used to diagnose type 1 diabetes, gestational diabetes or cystic fibrosis-related diabetes (NIDDK).
• Fasting plasma glucose and the oral glucose tolerance test can also diagnose type 2 diabetes and prediabetes. A blood glucose test may show diabetes when an A1C does not, or the other way round, which is why tests are repeated before a diagnosis (NIDDK). The fasting and glucose tolerance ranges are on fasting blood sugar levels.

Why A1C results can vary

• Test precision. A repeat test can come out slightly higher or lower. NIDDK's example: an A1C of 6.8 percent on one test could read anywhere from 6.4 to 7.2 percent on a repeat test of the same blood sample (NIDDK).
• Red blood cell changes. Conditions that change how long red blood cells live, such as recent blood loss, sickle cell disease, erythropoietin treatment, hemodialysis or transfusion, can change A1C levels (NIDDK). Before using A1C to diagnose diabetes, a doctor will consider pregnancy in the second or third trimester and certain types of anemia or other blood problems (NIDDK).
• Hemoglobin variants. Some hemoglobin variants can interfere with A1C, although most A1C tests used in the United States are not affected by the most common ones. If A1C and blood glucose results do not match, the A1C may not be a reliable test for you (NIDDK).
• Recent weeks count more. A1C does not show sudden, short-term ups and downs. Blood glucose in the past 30 days has a greater effect on the result than earlier months (NIDDK).

A1C goals for people with diabetes

NIDDK says experts recommend an A1C test at least twice a year for people with diabetes (NIDDK). Goals differ from person to person. Some people with diabetes can lower the risk of complications by keeping A1C below 7 percent, but that may not be safe if it leads to low blood glucose. A goal between 7 and 8 percent, or even higher in some cases, may suit people with limited life expectancy, long-standing diabetes and trouble reaching a lower goal, severe hypoglycemia or hypoglycemia unawareness, or advanced complications (NIDDK). MedlinePlus puts it as a goal below 7 for many people with diabetes, and says to ask your provider what yours should be (MedlinePlus).

A1C and average glucose

Some labs report an estimated average glucose (eAG) with the A1C. It converts the percentage into mg/dL, the units home meters use. It will not match daily readings because it is a long-term average (NIDDK). To convert a result yourself, use the A1C to average glucose calculator.

Should I get tested?

NIDDK says that if you have risk factors for prediabetes or diabetes, you should talk with your doctor about whether to be tested (NIDDK). The diabetes risk test looks at common risk factors; how it scores is in the diabetes risk test, explained.

Common questions

Is an A1C of 5.7 prediabetes?

Yes. NIDDK prints the prediabetes range as 5.7 to 6.4 percent, so 5.7 is the low end of it (NIDDK).

Can I eat before an A1C test?

Yes. You do not need to fast, so the blood can be drawn at any time of day (NIDDK) (NIDDK).

Can one high A1C mean I have diabetes?

Not on its own if you have no symptoms. NIDDK says the result should be confirmed with a repeat test on a different day (NIDDK).