An A1C level of 6.5% or above is considered high and falls into the diabetes range. The prediabetes range sits between 5.7% and 6.4%, while anything below 5.7% is normal. These cutoffs matter because each percentage point above normal represents a meaningful increase in your average blood sugar over the past two to three months, and in your risk for serious health complications.
What A1C Numbers Mean
The A1C test measures the percentage of your red blood cells that have glucose attached to them. Because red blood cells live for about three months, the test captures a rolling average of your blood sugar rather than a single snapshot. A normal A1C of 5.7% or below translates to an average blood sugar of roughly 117 mg/dL or less.
As the numbers climb, so does average blood sugar:
- 7% A1C corresponds to an average blood sugar around 154 mg/dL
- 8% A1C corresponds to roughly 183 mg/dL
- 9% A1C corresponds to roughly 212 mg/dL
- 10% A1C corresponds to roughly 240 mg/dL
At 240 mg/dL and above, the body can start producing ketones, toxic acids that build up in the blood and can lead to a dangerous condition called diabetic ketoacidosis. So an A1C of 10% or higher signals that blood sugar has been consistently in a zone where acute emergencies become a real possibility, not just long-term damage.
The Target for People With Diabetes
If you already have a diabetes diagnosis, the goal is generally to keep your A1C below 7%. The American Diabetes Association’s 2025 standards recommend this target for most non-pregnant adults, as long as reaching it doesn’t cause frequent episodes of dangerously low blood sugar. For some people, particularly older adults or those with other serious health conditions, a target of 8% or even slightly higher may be more appropriate. Your target depends on your age, how long you’ve had diabetes, and what other health issues are in the picture.
What Happens When A1C Stays High
Sustained high blood sugar damages blood vessels throughout the body, and the effects show up in predictable places. Small blood vessels in the eyes, kidneys, and nerves are especially vulnerable. Research published in Diabetes Care found that people with newly diagnosed type 2 diabetes whose A1C swung up and down by more than half a percentage point between visits had dramatically higher complication rates: up to 7.4 times the risk of diabetic eye disease, 5.2 times the risk of diabetic foot ulcers, and 3.5 times the risk of new kidney disease compared to those with stable readings. Keeping A1C consistently in range matters as much as hitting a specific number.
Cardiovascular risk also rises. High blood sugar accelerates the buildup of plaque in arteries, increasing the chance of heart attack and stroke. These large-vessel complications are the leading cause of death in people with type 2 diabetes, and they begin accumulating even in the prediabetes range.
Symptoms of Chronically High Blood Sugar
A high A1C itself doesn’t produce symptoms directly. What you feel are the effects of the elevated blood sugar it reflects. Most people don’t notice symptoms until blood sugar consistently exceeds about 180 to 200 mg/dL, and even then, the signs develop gradually over days or weeks. That slow onset is part of what makes high blood sugar dangerous: you can walk around with damaging levels for a long time without realizing it.
Early symptoms include frequent urination, increased thirst, blurred vision, and unusual fatigue. If blood sugar remains uncontrolled, more serious signs can develop, including fruity-smelling breath, nausea, abdominal pain, confusion, and shortness of breath. These later symptoms point toward ketoacidosis and require immediate medical attention.
How Often A1C Gets Checked
If your A1C is within your target range and your treatment plan is stable, testing every six months is typical. If your A1C is above target or your medications have recently changed, testing every three months gives you and your doctor a faster feedback loop to see whether adjustments are working. The three-month window matches the lifespan of red blood cells, so testing more frequently than that won’t give you meaningfully new information.
When A1C Results Can Be Misleading
The test isn’t perfect for everyone. Certain conditions change how long red blood cells survive or how easily glucose attaches to them, which can push your A1C reading artificially higher or lower than your actual blood sugar average.
Iron deficiency anemia, chronic kidney disease, and certain inherited blood cell conditions (like sickle cell trait) can all skew results. African American individuals may have genetically higher A1C levels that don’t fully correspond to their blood sugar. Age also plays a role: A1C tends to drift upward with aging independent of actual glucose control. Some HIV medications can push A1C readings lower than expected.
If your A1C doesn’t match what your daily blood sugar readings suggest, your doctor may use a different test, such as a fructosamine test or an oral glucose tolerance test, to get a clearer picture. This is especially worth flagging if you have any of the conditions above, because treatment decisions based on an inaccurate A1C could lead to under- or over-treatment.