An A1C of 6.5% or higher means diabetes. This is the standard threshold used to diagnose type 2 diabetes, and it represents an estimated average blood sugar of about 140 mg/dL over the previous two to three months. Below that, an A1C between 5.7% and 6.4% falls in the prediabetes range, and anything under 5.7% is considered healthy.
How the A1C Ranges Break Down
The A1C test measures how much glucose has attached to your red blood cells’ hemoglobin, a protein that carries oxygen through your bloodstream. Because red blood cells live about three months, the test captures a rolling average of your blood sugar over that window rather than a single moment in time. That makes it more stable than a finger-stick reading, which can swing depending on what you ate an hour ago.
The three categories are straightforward:
- Below 5.7%: Healthy. This corresponds to an average blood sugar around 117 mg/dL or lower.
- 5.7% to 6.4%: Prediabetes. Blood sugar is running higher than normal but hasn’t crossed the diabetes line yet.
- 6.5% or higher: Diabetes. At 6.5%, estimated average blood sugar is roughly 140 mg/dL. At 7.0%, it’s about 154 mg/dL.
These thresholds come from the American Diabetes Association’s diagnostic criteria, which were most recently reaffirmed in their 2024 Standards of Care.
Why a Single Test Usually Isn’t Enough
A reading of 6.5% on one test doesn’t automatically lock in a diabetes diagnosis. Current guidelines call for a second abnormal result to confirm it. That can be a repeat A1C on a different day or a different type of blood sugar test, like a fasting glucose. If both come back above the threshold, the diagnosis is confirmed. For example, an initial A1C of 7.0% followed by a repeat of 6.8% would confirm diabetes.
The one exception: if you already have obvious symptoms of high blood sugar (excessive thirst, frequent urination, unexplained weight loss) along with a very high random blood sugar reading, a single test may be enough.
What Prediabetes Means in Practice
Landing between 5.7% and 6.4% is a warning, not a sentence. Prediabetes means your body is losing its ability to manage blood sugar efficiently, but the damage is still largely reversible. Losing 5% to 7% of body weight and adding regular physical activity can significantly reduce the chances of progressing to type 2 diabetes. The higher your A1C sits within that range, the more urgently those changes matter.
If you’re in the prediabetes range, your doctor will typically retest every one to two years to see whether your numbers are trending up, holding steady, or improving.
How Often the Test Is Repeated
For people already diagnosed with diabetes, how frequently you get tested depends on how well your blood sugar is controlled. If you’re still working toward a stable target, testing every three months lets you and your doctor see whether treatment adjustments are working. Once your levels are consistently on target, testing every six months is the standard recommendation. The test doesn’t require fasting, so it can be done at any routine blood draw.
When the A1C Can Be Wrong
The test is reliable for most people, but certain conditions can push the result artificially high or low. This matters because a misleading number could lead to a missed diagnosis or an unnecessary one.
Conditions that can make your A1C read falsely high include iron deficiency anemia, vitamin B12 or folate deficiency, chronic kidney disease, and chronic heavy alcohol use. In these cases, your actual average blood sugar may be lower than the test suggests.
Conditions that can make your A1C read falsely low include pregnancy (especially early or late stages), recent blood loss or transfusions, sickle cell anemia, thalassemia, and certain stages of kidney disease. Hemoglobin variants, which are more common in people of African, Mediterranean, and Southeast Asian descent, can skew results in either direction depending on the lab method used.
If your A1C doesn’t match what your daily glucose readings or symptoms suggest, your doctor may use a different test to get a clearer picture. Fasting glucose and oral glucose tolerance tests measure blood sugar directly rather than through hemoglobin, so they aren’t affected by the same issues.
A1C Targets After Diagnosis
Once you have a diabetes diagnosis, the goal for most adults is to keep A1C below 7.0%, which translates to an average blood sugar of about 154 mg/dL. Some people aim for a tighter target (closer to 6.5%), while others with a long history of diabetes, older age, or other health conditions may have a slightly more relaxed goal. The right target depends on your individual situation, including how prone you are to low blood sugar episodes.
Each percentage point drop in A1C meaningfully reduces the risk of complications affecting the eyes, kidneys, and nerves. Moving from 8.0% to 7.0%, for instance, represents a significant reduction in long-term damage even though the numbers seem close together. Small, sustained improvements matter more than dramatic short-term changes.