What fasting plasma glucose level defines diabetes when confirmed on a separate day?

• A. 140 mg/dL
• B. 100 mg/dL
• C. 126 mg/dL or higher
• D. 110 mg/dL

Answer: (C)

Diagnosing diabetes with fasting plasma glucose relies on a clear threshold that shows persistent fasting hyperglycemia. The cutoff is 126 mg/dL or higher, but it must be confirmed on a separate day to rule out a one‑time fluctuation from illness, stress, or lab variance. Between 100 and 125 mg/dL is considered impaired fasting glucose, a prediabetes range, not diabetes. So a single test hitting 126 mg/dL isn’t enough by itself; the second fasting test on another day also needs to be 126 mg/dL or higher to make the diagnosis. The other numbers don’t fit because they fall outside the diabetes threshold for fasting glucose: 100 mg/dL sits in the normal/prediabetes range, 110 mg/dL isn’t a diagnostic criterion, and 140 mg/dL relates to other testing contexts, not the fasting glucose criterion for diabetes.