Hemoglobin A1C above 5.7% is high. Specifically, 5.7-6.4% indicates prediabetes and 6.5% or higher meets the threshold for diabetes. The number reflects your average blood glucose over the past 8-12 weeks, and the higher it climbs, the greater your risk of long-term complications. Here is what your reading means and how to bring it down.
What A1C Measures and Why It Matters
The hemoglobin A1C test (also called HbA1c or glycated hemoglobin) measures the percentage of your red blood cells that have glucose attached to the hemoglobin protein. Because red blood cells live about 120 days, A1C captures average glucose over roughly 3 months — a much fuller picture than a single fingerstick reading.
| A1C % | Estimated Average Glucose (mg/dL) | Category |
|---|---|---|
| 5.0% | 97 | Normal |
| 5.6% | 114 | Normal (high end) |
| 5.7% | 117 | Prediabetes begins |
| 6.0% | 126 | Prediabetes |
| 6.4% | 137 | Prediabetes (high end) |
| 6.5% | 140 | Diabetes begins |
| 7.0% | 154 | Diabetes (treatment target) |
| 8.0% | 183 | Above target |
| 9.0% | 212 | Significantly above target |
| 10.0% | 240 | Poorly controlled |
For more on interpreting A1C, see our A1C levels guide and try our A1C calculator.
What Causes High A1C
High A1C develops when blood glucose runs above target most of the day for weeks or months. Drivers include:
- Insulin resistance — cells stop responding well to insulin
- Excess body weight, especially abdominal fat
- Inactivity — muscle is the body’s largest glucose disposal site
- Diet patterns high in refined carbs, sweetened beverages, and ultra-processed foods
- Family history and genetics
- Aging — insulin sensitivity declines after age 45
- Sleep deprivation (less than 6 hours nightly)
- Chronic stress and elevated cortisol
- Medications — corticosteroids, some diuretics, certain antipsychotics
- Pregnancy (gestational diabetes)
- PCOS, Cushing’s syndrome, and other endocrine conditions
Dangers of High A1C by Level
5.7-6.4% (Prediabetes)
Risk of progressing to diabetes is roughly 5-10% per year if untreated. Heart disease and stroke risk start to rise. Many people are asymptomatic, but insulin resistance is already affecting blood vessels and the liver.
6.5-7.5% (Mild Diabetes)
Long-term complication risk begins to climb. Studies show every 1% rise in A1C above 6.5% increases cardiovascular risk by about 14% and kidney disease risk by about 30%. Symptoms like fatigue, blurred vision, and frequent urination may appear.
7.6-9% (Above Target)
Risk of microvascular complications (retinopathy, neuropathy, nephropathy) accelerates. Wound healing slows. Infections become more common. Most providers intensify treatment at this level.
Above 9%
Significantly elevated risk of all complications. According to the CDC, sustained A1C above 9% is associated with substantial increases in heart attack, stroke, kidney failure, and amputation rates.
How to Lower High A1C
Diet
- Reduce refined carbs, added sugars, and sweetened drinks
- Build meals around non-starchy vegetables, lean protein, and healthy fat
- Choose whole grains and legumes over white bread and rice
- Aim for 25-35 grams of fiber per day
- Eat fruit whole rather than as juice
Activity
- 150 minutes of moderate aerobic activity weekly (brisk walking, cycling, swimming)
- Two days of resistance training
- 10-minute walk after meals to blunt post-meal spikes
- Break up sitting every 30 minutes
Weight
- Losing 5-7% of body weight can lower A1C by 0.5-1.0 points
- Sustained loss matters more than rapid loss
Sleep and Stress
- 7-9 hours of sleep nightly
- Manage stress with mindfulness, therapy, or social support
- Treat sleep apnea if present
Medications
Metformin is the most common first-line medication for prediabetes that does not respond to lifestyle change. Other classes (GLP-1 receptor agonists, SGLT2 inhibitors) may be considered depending on weight, kidney function, and cardiovascular risk. Your doctor will tailor choices to you.
Read more on lowering high readings in our high A1C levels guide.
How Often Should You Recheck?
| Status | Recheck Frequency |
|---|---|
| A1C 5.7-6.4% (prediabetes), no medication | Every 6-12 months |
| A1C 6.5%+ at goal | Every 6 months |
| A1C 6.5%+ above goal or treatment changed | Every 3 months |
| Pregnant or planning pregnancy | Per provider, more often |
Things That Can Falsely Affect Your A1C
A1C results can be misleading in certain conditions:
- Anemia (iron-deficiency, B12) — may falsely raise A1C
- Recent blood loss or transfusion — may falsely lower
- Hemoglobin variants (sickle cell trait, thalassemia) — can interfere with the test
- Chronic kidney or liver disease — alters red cell turnover
- Pregnancy — A1C runs slightly lower
If your A1C does not match your daily glucose readings, ask your provider whether one of these factors applies.
The Bottom Line
A hemoglobin A1C above 5.7% is high and deserves attention — even at the prediabetes level. The number reflects average glucose over 8-12 weeks, and lowering it through diet, activity, weight loss, and sleep can dramatically reduce the risk of progressing to type 2 diabetes and developing complications. Most people see meaningful improvement within 3-6 months of consistent change. Talk to your provider about a recheck schedule and whether medication is appropriate for you.
