An HbA1c of 6.5% or higher means diabetes. Below 5.7% is normal, and anything between 5.7% and 6.4% falls in the prediabetes range. This single blood test captures your average blood sugar over the past two to three months, making it one of the most reliable tools for diagnosing and monitoring diabetes.
The Diagnostic Ranges
The CDC uses three clear cutoffs for HbA1c results:
- Normal: below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or above
A result of 6.5% typically needs to be confirmed with a second test on a different day before a formal diagnosis is made. If you’re in the prediabetes range, that’s a signal your blood sugar is running higher than it should, but lifestyle changes at this stage can often prevent progression to type 2 diabetes.
What HbA1c Actually Measures
Hemoglobin is the protein inside red blood cells that carries oxygen. When glucose circulates in your blood, some of it naturally sticks to hemoglobin through a chemical bonding process. The more glucose in your blood over time, the more hemoglobin gets coated. HbA1c measures the percentage of your hemoglobin that has glucose attached to it.
Red blood cells live for roughly 120 days. Once glucose bonds to hemoglobin, it stays there for the life of that cell. This is why the test reflects a two-to-three-month average rather than a single moment in time. It won’t be thrown off by what you ate yesterday or a stressful morning, which makes it more stable than a finger-prick glucose reading.
What Your Number Means in Daily Terms
An HbA1c percentage can feel abstract. Converting it to an estimated average glucose (eAG) gives you a number that looks more like what you’d see on a home glucose meter. Here’s how common HbA1c values translate:
- 5% = average blood sugar of about 97 mg/dL
- 6% = about 126 mg/dL
- 7% = about 154 mg/dL
- 8% = about 183 mg/dL
- 9% = about 212 mg/dL
- 10% = about 240 mg/dL
So an HbA1c of 6.5%, the diabetes threshold, corresponds to an average blood sugar of roughly 140 mg/dL over the previous few months. Each 1% increase in HbA1c adds approximately 29 mg/dL to your estimated average.
The Target for People With Diabetes
Getting diagnosed at 6.5% doesn’t mean you need to stay there. The American Diabetes Association recommends that most adults with diabetes aim for an HbA1c below 7%, which translates to an average blood sugar under about 154 mg/dL. That target is associated with a significantly lower risk of complications affecting the eyes, kidneys, and nerves.
Your personal target may differ. Older adults, people with other serious health conditions, or those at high risk of dangerous blood sugar drops may be given a slightly more relaxed goal. Younger, otherwise healthy people might aim tighter, closer to 6.5%. The right number depends on your overall health picture, not just the diabetes itself.
How Often to Get Tested
If your blood sugar is well controlled and you’re meeting your treatment goals, testing every six months is generally enough. If your treatment has recently changed, or you’re struggling to keep blood sugar in range, every three months is more appropriate. Since the test reflects a rolling two-to-three-month window, testing more frequently than every three months won’t give you meaningfully new information.
When the Test Can Be Inaccurate
HbA1c is reliable for most people, but certain conditions can skew results in either direction. Anything that shortens the lifespan of red blood cells, like hemolytic anemia or significant recent blood loss, will make your HbA1c appear falsely low. Your red blood cells simply haven’t been around long enough to accumulate a representative amount of glucose.
Iron deficiency anemia pushes results in the opposite direction, making HbA1c appear falsely high. This is particularly relevant during late pregnancy, when iron deficiency is common and can inflate HbA1c readings even in women without diabetes. Kidney failure can also interfere with test accuracy because chemical changes to hemoglobin in that condition affect how the test reads the sample.
People with sickle cell trait or other hemoglobin variants may get unreliable results depending on the specific lab method used. If you have any of these conditions, your doctor may rely on alternative measures of blood sugar control, such as a fructosamine test or continuous glucose monitoring, instead of HbA1c alone.