A normal A1C level is below 5.7%. Results between 5.7% and 6.4% indicate prediabetes, and an A1C of 6.5% or higher signals diabetes. These thresholds apply to most adults, though several factors can shift your number independent of actual blood sugar control.
What the A1C Test Measures
The A1C test measures how much glucose has attached to hemoglobin, the oxygen-carrying protein inside your red blood cells. When blood sugar rises, more glucose sticks to hemoglobin, and it stays there for the entire life of the cell. Since red blood cells live about three months, the test captures your average blood sugar over that window rather than a single moment in time.
This makes A1C a broader snapshot than a finger-stick glucose reading, which only tells you what’s happening right now. It also means the test doesn’t require fasting. You can eat normally before the blood draw.
What Each Range Means
The three categories are straightforward:
- Below 5.7%: Normal. Your blood sugar regulation is working well.
- 5.7% to 6.4%: Prediabetes. Blood sugar is elevated but not high enough for a diabetes diagnosis. This is the stage where lifestyle changes (diet, exercise, weight loss) are most effective at preventing progression.
- 6.5% or higher: Diabetes. This result, confirmed on a second test, meets the diagnostic threshold for type 2 diabetes.
To put these percentages in concrete terms, you can convert A1C to an estimated average glucose. A 6% A1C corresponds to an average blood sugar of about 126 mg/dL. At 7%, that average climbs to 154 mg/dL. By 9%, you’re looking at roughly 212 mg/dL. The formula is simple: multiply the A1C by 28.7, then subtract 46.7. A normal A1C of 5% works out to an average blood sugar around 97 mg/dL.
Targets Differ for People Already Managing Diabetes
If you’ve been diagnosed with diabetes, “normal” isn’t necessarily your goal. Most adults with diabetes aim for an A1C below 7%, which reflects an average blood sugar of about 154 mg/dL. But that target gets adjusted based on age, overall health, and the risk of blood sugar dropping too low.
For healthy older adults, a target below 7.5% is common. For older adults with significant health conditions or a life expectancy under ten years, targets relax further, often to 8% or even 8.5%. At 8.5%, average blood sugar sits around 200 mg/dL. The reasoning: pushing for tight control in someone who is frail or managing multiple conditions increases the risk of dangerous blood sugar crashes without offering enough long-term benefit to justify it.
When the Test Can Be Inaccurate
The A1C test assumes your red blood cells have a normal lifespan and structure. Anything that changes how long those cells live or how hemoglobin behaves can throw off the result. Conditions that falsely raise or lower your A1C include:
- Severe anemia: Changes red blood cell turnover, distorting the three-month average.
- Blood disorders: Sickle cell disease, sickle cell trait, and thalassemia alter hemoglobin structure. These conditions tend to lower A1C values, potentially masking high blood sugar.
- Kidney or liver disease: Both can interfere with red blood cell lifespan or hemoglobin chemistry.
- Recent blood loss or transfusions: Introduces new red blood cells that haven’t had time to accumulate glucose, artificially lowering results.
- Certain medications: Opioids and some HIV medications can affect results.
- Pregnancy: Both early and late pregnancy can skew the number.
If any of these apply to you, your provider may use an alternative test, such as a fructosamine test, which measures blood sugar over a shorter two-to-three-week window using a different protein.
Race and Ethnicity Can Affect Results
A growing body of research shows that A1C doesn’t perform equally across all populations. African American individuals consistently have higher A1C levels than white individuals at the same actual blood sugar, regardless of whether their glucose tolerance is normal, prediabetic, or diabetic. A CDC-published review found that the standard A1C cutoffs increased the risk of false positives (overdiagnosis) in African American populations compared with white populations.
The reverse can also happen. In some African and Afro-Caribbean populations, the 6.5% cutoff missed actual diabetes cases, leading to underdiagnosis. Part of this variation traces to genetic factors: a common enzyme deficiency (G6PD deficiency), which is more prevalent in people of African descent, is associated with lower A1C values. Sickle cell trait has a similar effect. But genetics don’t fully explain the gap. Chronic stress, socioeconomic factors, and inflammation also appear to play a role.
This matters practically. If you’re in one of these groups and your A1C sits right at a diagnostic boundary, a glucose-based test (like a fasting glucose or oral glucose tolerance test) can give a more reliable picture.
How Often to Get Tested
If your A1C is normal and you have no risk factors, testing every three years starting at age 35 is a reasonable schedule. If you’re in the prediabetes range, annual testing helps track whether your blood sugar is stable, improving, or creeping higher. People with diagnosed diabetes typically get tested two to four times per year, depending on how well controlled their levels are and whether their treatment has recently changed.
Because the test reflects a three-month average, checking more often than every three months won’t give you meaningfully new information. A result taken six weeks after a major diet change, for example, still partially reflects your blood sugar from before you made the change.