Prediabetes A1C Range
The prediabetes range for A1C is 5.7% to 6.4%, as established by the American Diabetes Association. 1, 2
Diagnostic Criteria
The American Diabetes Association formally defines prediabetes using the following A1C threshold 1, 2:
- A1C: 5.7–6.4% (39–47 mmol/mol)
This range was established based on systematic reviews demonstrating that individuals with A1C between 5.5% and 6.0% have a 5-year diabetes incidence of 9-25%, while those with A1C between 6.0-6.5% have a 5-year risk of 25-50% 1. The 5.7% lower threshold was chosen because it corresponds to diabetes risk similar to high-risk participants in the Diabetes Prevention Program 1, 2.
Risk Stratification Within the Prediabetes Range
Risk increases disproportionately at the higher end of the prediabetes spectrum 1, 2:
- A1C 5.7-6.0%: Moderately increased risk with 5-year diabetes incidence of 9-25% 3
- A1C 6.0-6.4%: Very high risk with 5-year diabetes incidence of 25-50% and relative risk 20 times higher compared to A1C of 5.0% 1, 3
Due to this gradient, individuals with A1C above 6.0% should receive the most intensive interventions and particularly vigilant follow-up 1, 2.
Clinical Context and Alternative Definitions
It is important to note that the World Health Organization and some international diabetes organizations define impaired fasting glucose starting at 110 mg/dL (6.1 mmol/L) rather than 100 mg/dL, which corresponds to a slightly higher A1C threshold 1. However, the ADA's 5.7% lower limit remains the standard in U.S. practice.
Important Caveats
A1C-defined prediabetes does not perfectly overlap with glucose-defined prediabetes (impaired fasting glucose or impaired glucose tolerance). Studies show that using A1C alone would miss a substantial number of patients who have glucose-based prediabetes 4, 5. The positive predictive value of A1C 5.7-6.4% for confirming prediabetes by oral glucose tolerance test is only approximately 39% in some clinical populations 5.
Despite this limitation, A1C remains a valid screening tool because it is a stronger predictor of future diabetes and cardiovascular events than fasting glucose in many populations 1, 2, and baseline A1C strongly predicts diabetes development even when using glucose-based diagnostic criteria 1.
Clinical Management Implications
All individuals with A1C in the prediabetic range should be 1, 2:
- Informed of their increased risk for both diabetes and cardiovascular disease
- Counseled about effective preventive strategies, particularly weight loss and physical activity
- Monitored regularly, with more frequent follow-up for A1C >6.0%
Evidence from the Diabetes Prevention Program demonstrates that lifestyle interventions are effective across the entire prediabetic A1C range 1, 2.