A1c Range for Prediabetes Diagnosis
An A1c level of 5.7% to 6.4% (39-47 mmol/mol) qualifies an adult as having prediabetes according to the American Diabetes Association Standards of Care. 1
Diagnostic Criteria
The most recent ADA guidelines (2023) define prediabetes using three possible criteria, any one of which qualifies for the diagnosis 1:
- A1c: 5.7–6.4% (39–47 mmol/mol) 1
- Fasting plasma glucose: 100-125 mg/dL (5.6-6.9 mmol/L) 1
- 2-hour plasma glucose during 75-g OGTT: 140-199 mg/dL (7.8-11.0 mmol/L) 1
Evidence Supporting the A1c Threshold
The 5.7% lower cutoff is based on robust prospective data demonstrating substantial diabetes risk 1:
- A1c 5.5-6.0%: 5-year diabetes incidence of 9-25%, representing a substantially increased risk 1, 2
- A1c 6.0-6.5%: 5-year diabetes incidence of 25-50%, with a relative risk 20 times higher compared to A1c of 5.0% 1, 2
- A1c ≥5.7%: Associated with diabetes risk similar to high-risk participants in the Diabetes Prevention Program 1
A systematic review of 44,203 individuals from 16 cohort studies with average 5.6-year follow-up confirmed this continuous, steep relationship between A1c and subsequent diabetes development 1.
Important Clinical Caveats
Risk is continuous across the entire range, extending below 5.7% and becoming disproportionately greater at the higher end 1. This means:
- Patients with A1c 5.5-5.6% still have elevated risk (though not formally classified as prediabetes) 1, 2
- Those with A1c 6.0-6.4% warrant more aggressive preventive intervention than those at 5.7-5.9% 1, 2
International variation exists: The World Health Organization defines impaired fasting glucose starting at 110 mg/dL (6.1 mmol/L) rather than 100 mg/dL, which may affect how different organizations approach prediabetes screening 1.
Screening Recommendations
Testing for prediabetes should be considered in 1:
- All adults starting at age 45 years 1
- Adults of any age with BMI ≥25 kg/m² (≥23 kg/m² in Asian Americans) plus one or more risk factors including first-degree relative with diabetes, high-risk race/ethnicity, history of cardiovascular disease, hypertension, dyslipidemia, polycystic ovary syndrome, or physical inactivity 1
- Annual testing for those already diagnosed with prediabetes 1
A1c, fasting plasma glucose, and 2-hour OGTT are equally appropriate for screening and diagnosis 1. In community-based studies, baseline A1c was actually a stronger predictor of subsequent diabetes and cardiovascular events than fasting glucose 1.
Practical Limitations
While the A1c threshold of 5.7-6.4% is well-established in guidelines, research suggests this approach may miss a substantial proportion of individuals with glucose-defined prediabetes, with sensitivity concerns particularly in certain racial groups 3. However, the ADA guidelines remain the standard of care for clinical practice 1.