Which value obtained during a glucose tolerance test is diagnostic of diabetes mellitus?

• A. 2 hr. specimen = 150 mg/dL (8.3 mmol/L)
• B. fasting plasma glucose = 126 mg/dL (6.9 mmol/L)
• C. fasting plasma glucose = 110 mg/dL (6.1 mmol/L)
• D. 2 hr. specimen = 180 mg/dL (9.9 mmol/L)

Answer: (B)

A value for diagnosing diabetes is a fasting plasma glucose of 126 mg/dL (7.0 mmol/L) or higher, or a 2-hour post-load glucose of 200 mg/dL (11.1 mmol/L) or higher after an oral glucose tolerance test. The 126 mg/dL fasting value meets the diabetes threshold, making it diagnostic. The other values do not: 110 mg/dL is within normal to impaired fasting glucose range, and 2-hour values of 150 mg/dL and 180 mg/dL are in the impaired glucose tolerance range (140–199 mg/dL) but below the diabetes threshold of 200 mg/dL.