HbA1c Cut Points for Prediabetes and Type 2 Diabetes
In adults, prediabetes is defined as HbA1c 5.7–6.4% (39–47 mmol/mol), and type 2 diabetes is diagnosed at HbA1c ≥6.5% (≥48 mmol/mol). 1
Diagnostic Thresholds
Prediabetes: HbA1c 5.7–6.4%
The American Diabetes Association establishes the prediabetes range at 5.7% to 6.4% 1, 2, 1. This range identifies individuals at substantially increased risk for progression to diabetes:
- HbA1c 5.5–6.0%: 5-year diabetes incidence of 9–25%
- HbA1c 6.0–6.5%: 5-year diabetes incidence of 25–50%, with a relative risk 20 times higher than HbA1c of 5.0% 1
The 5.7% lower threshold was specifically chosen because it identifies individuals with diabetes risk similar to high-risk participants in the Diabetes Prevention Program, making them ideal candidates for intensive lifestyle intervention 1, 3.
Type 2 Diabetes: HbA1c ≥6.5%
Type 2 diabetes is diagnosed at HbA1c ≥6.5% (≥48 mmol/mol) 1, 2, 1. This threshold should be confirmed with repeat testing unless the patient presents with unequivocal hyperglycemia or hyperglycemic crisis 4.
Important Clinical Considerations
Risk Continuum
Risk is continuous across all HbA1c values, extending below the lower limit of the prediabetes range and becoming disproportionately greater at the higher end 1, 2, 1. This means:
- Individuals with HbA1c >6.0% warrant more aggressive intervention and closer follow-up
- Those with both elevated HbA1c and abnormal fasting glucose represent the highest-risk group requiring immediate action
International Variation
The World Health Organization and some international organizations define prediabetes starting at HbA1c 6.0% rather than 5.7% 1. However, the ADA's 5.7% threshold captures more individuals who would benefit from early intervention, particularly for lifestyle modification programs 5, 6.
Confirmation Testing
When HbA1c results are discordant with other glucose measures, repeat the test that exceeded the diagnostic threshold. If two different tests both exceed their respective thresholds (e.g., both HbA1c ≥6.5% and fasting glucose ≥126 mg/dL), diabetes is confirmed without additional testing 4.
Testing Limitations
HbA1c may be unreliable in certain conditions affecting red blood cell turnover, including hemoglobinopathies, recent blood loss, hemolytic anemia, or pregnancy 3. In these situations, use glucose-based criteria instead.
Screening Frequency
For adults with normal test results, repeat screening at minimum 3-year intervals. More frequent testing is appropriate when BMI is increasing or risk factors are worsening 1.