A1c 6.4%
A1c of 6.4%: what it means
An A1c of 6.4% is the top of the prediabetes range, one tenth of a point below the diabetes threshold.
Average glucose from the ADAG formula, eAG = 28.7 × A1c − 46.7 (Nathan 2008). Categories from the ADA Standards of Care (ADA Standards 2026, sec. 2).
What an A1c of 6.4% means
- The ADA defines prediabetes by A1c as 5.7% to 6.4%, and diabetes as 6.5% or higher. (ADA Standards 2026, sec. 2)
- Repeat tests on the same sample vary a little. NIDDK gives the example that a result of 6.8% could read anywhere from 6.4% to 7.2% on a repeat test. (NIDDK)
- Within the prediabetes range of 5.7% to 6.4%, the higher the A1c, the higher the risk of developing type 2 diabetes. (NIDDK)
- Without symptoms, a result in the prediabetes or diabetes range is usually repeated on a different day, with A1c or another glucose test, before a diagnosis is made. (NIDDK)
- In the Diabetes Prevention Program trial, adults with raised glucose who joined an intensive lifestyle program (weight loss and about 150 minutes of activity a week) developed type 2 diabetes 58% less often than the placebo group over an average of 2.8 years. (DPP 2002)
An A1c of 6.4% is 0.1 points below the diabetes threshold of 6.5% (140 mg/dL) and 0.8 points above the top of the normal range.
Questions to ask your doctor
- Should this result be confirmed with a repeat A1c or a different glucose test?
- When should I be tested again?
- Is a lifestyle change program, such as a diabetes prevention program, a good fit for me?
- Could anything make my A1c less accurate, such as anemia or a hemoglobin variant?
Nearby values
| A1c | mg/dL | mmol/L | Category |
|---|---|---|---|
| 5.9% | 123 | 6.8 | Prediabetes |
| 6.0% | 126 | 7.0 | Prediabetes |
| 6.1% | 128 | 7.1 | Prediabetes |
| 6.2% | 131 | 7.3 | Prediabetes |
| 6.3% | 134 | 7.4 | Prediabetes |
| 6.4% | 137 | 7.6 | Prediabetes |
| 6.5% | 140 | 7.8 | Diabetes |
| 6.6% | 143 | 7.9 | Diabetes |
| 6.7% | 146 | 8.1 | Diabetes |
| 6.8% | 148 | 8.2 | Diabetes |
| 6.9% | 151 | 8.4 | Diabetes |
All values from 4.0% to 14.0% are in the A1c chart. Planning a retest? See how fast A1c can change. Over 65? See A1c by age.
Try another number
Estimated average glucose (eAG) = 28.7 × A1c − 46.7, from the ADAG study. mmol/L = mg/dL ÷ 18.016. Real averages vary from person to person at the same A1c. This is a conversion, not a diagnosis.
Other key numbers
6.5 mmol/L
6.6 mmol/L
6.8 mmol/L
7.0 mmol/L
7.1 mmol/L
7.3 mmol/L
7.4 mmol/L
7.8 mmol/L
8.6 mmol/L
9.4 mmol/L
10.2 mmol/L
10.9 mmol/L
11.7 mmol/L
13.3 mmol/L
14.9 mmol/L
16.5 mmol/L
Sources
- Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ; A1c-Derived Average Glucose (ADAG) Study Group. Translating the A1C assay into estimated average glucose values. Diabetes Care. 2008;31(8):1473-1478. doi.org/10.2337/dc08-0545
- American Diabetes Association Professional Practice Committee. 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes 2026. Diabetes Care. 2026;49(Suppl 1). doi.org/10.2337/dc26-S002
- National Institute of Diabetes and Digestive and Kidney Diseases (NIH). The A1C Test & Diabetes. www.niddk.nih.gov/health-information/diagnostic-tests/a1c-test
- Diabetes Prevention Program Research Group (Knowler WC, et al.). Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. N Engl J Med. 2002;346(6):393-403. doi.org/10.1056/NEJMoa012512
Written and maintained by the controla1clevels.com editorial team. We do not have a medical reviewer; every claim links to its primary source above. Last reviewed: 2026-10-25. Spotted an error? See About.