What are the ADA diagnostic thresholds for diabetes using A1c, FPG, and OGTT?

• A. A1c ≥6.5%; FPG ≥126 mg/dL; 2-hour OGTT ≥200 mg/dL
• B. A1c ≥7.0%; FPG ≥130 mg/dL; 2-hour OGTT ≥180 mg/dL
• C. A1c ≥6.0%; FPG ≥110 mg/dL; 2-hour OGTT ≥190 mg/dL
• D. A1c ≥5.7%; FPG ≥100 mg/dL; 2-hour OGTT ≥140 mg/dL

Answer: (A)

Diagnosing diabetes with ADA criteria relies on three independent measurements, each with its own clear cutoff. An A1c of 6.5% or higher is diagnostic, meaning the average blood glucose over the past 2–3 months is high enough to meet diabetes criteria. A fasting plasma glucose of 126 mg/dL or higher is another path to the same conclusion, indicating elevated glucose after an overnight fast. The third route uses the oral glucose tolerance test: after a 75 g glucose drink, a 2-hour plasma glucose of 200 mg/dL or higher confirms diabetes.

These thresholds can diagnose diabetes if any one test meets or exceeds the cutoffs, though clinicians often confirm with a repeat test on a different day if results are uncertain or if there are no classic symptoms. The other sets of numbers don’t align with ADA criteria (for example, using 7.0% or 130 mg/dL or 180 mg/dL would not correctly identify the diabetes threshold). For broader context, lower cutoffs define prediabetes: A1c 5.7–6.4%, FPG 100–125 mg/dL, or 2-hour OGTT 140–199 mg/dL.