If you have ever been told to "get your HbA1c checked," you may have wondered what the test actually measures. In short, HbA1c shows your average blood sugar over the past two to three months, not just how it looked this morning.

How the test works

When sugar (glucose) circulates in your blood, some of it sticks to hemoglobin, the protein in red blood cells that carries oxygen. The more sugar in your blood, the more hemoglobin gets coated. Red blood cells live about three months, so the test reflects a long-term average. The result is shown as a percentage.

Typical result ranges

• Below 5.7%: usually considered normal
• 5.7% to 6.4%: usually called prediabetes
• 6.5% or higher: usually consistent with diabetes, often confirmed with a repeat test

Labs and doctors may use slightly different cut-offs, so always go by the range printed on your own report.

Do you need to fast?

No. HbA1c does not require fasting, so you can eat normally and test at any time of day. This is one reason doctors like it.

Things that can affect the result

• Anemia or recent blood loss
• Some inherited hemoglobin variants
• Kidney or liver disease
• Pregnancy

In these situations, a doctor may use other tests, such as fasting glucose, to check the picture.

Questions to ask your doctor

• What target is right for me?
• How often should I repeat the test?
• Should I also check fasting blood sugar or kidney function?

This article is for general education and is not medical advice. Please read our Disclaimer and talk to your doctor about your own results.

Sources to explore: American Diabetes Association, MedlinePlus (U.S. National Library of Medicine), World Health Organization.

HbA1c shows your average blood sugar over about three months. Learn the normal range, what prediabetes and diabetes results mean, and how to prepare.