The A1C Test for Diabetes and Prediabetes: What It Measures and What the Numbers Mean

The A1C test — also called the hemoglobin A1C or HbA1c test — is a simple blood test. It is used to diagnose prediabetes and diabetes, and to follow how well diabetes is being managed.

What it measures

Checking blood sugar at home gives a snapshot of a single moment, and blood sugar changes all the time. The A1C test instead reflects average blood sugar over the past 3 months.

When sugar enters the bloodstream, it attaches to hemoglobin, a protein in red blood cells. Everyone has some sugar-coated hemoglobin, but people with higher blood sugar have more. The test measures the percentage of red blood cells carrying it. Because red blood cells are replaced roughly every 3 months, the result reflects that period.

It does not replace home monitoring: it still matters to know how blood sugar moves through the day so you can adjust as you go.

Having the test

The test is done in a doctor's office or a lab, with blood drawn from a finger or arm. You don't need to fast, though a doctor may order other tests at the same time, such as cholesterol, that do require fasting.

Get an A1C test if you are over 45. It is also recommended for younger people who have overweight and any other risk factor for prediabetes and type 2 diabetes.

What happens next

• Normal result. Your doctor will suggest when to test again, based on your age and risk factors.
• Prediabetes. You can start right away on steps to reverse prediabetes, or to prevent or delay type 2 diabetes; talk to your doctor about how. You will probably be retested every 1 to 2 years.
• Diabetes. Your doctor will explain how to manage it with lifestyle changes and perhaps medicine. Most people with diabetes have an A1C test at least twice a year, and some need it more often depending on their management plan or other conditions.

The ranges

For people with diabetes, A1C also gives an estimate of average blood sugar, though it may not capture spikes or lows:

Goals

For most people with diabetes, the goal is an A1C of 7% or less; a doctor sets each person's goal from their full medical history. Higher A1C levels are linked to complications, so reaching and staying at the goal is central to living well with diabetes. With lifestyle changes, and medicine if prescribed, some people with diabetes reach an A1C below 6.5%. That does not mean the diabetes has gone — but it usually means blood sugar is well managed.

What can make the result wrong

Several things can falsely raise or lower an A1C result:

• severe anemia;
• kidney failure;
• liver disease;
• certain blood disorders, such as sickle cell anemia or thalassemia;
• certain medicines, including opioids and some HIV medications;
• blood loss or blood transfusions;
• early or late pregnancy.

Tell your doctor if any of these apply to you.

Sources

• Centers for Disease Control and Prevention, "A1C Test for Diabetes and Prediabetes": https://www.cdc.gov/diabetes/diabetes-testing/prediabetes-a1c-test.html
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