Common diagnostic criteria for diabetes mellitus include which thresholds?

• A. Fasting plasma glucose ≥126 mg/dL, HbA1c ≥6.5%, 2-hour plasma glucose ≥200 mg/dL during an OGTT, or random plasma glucose ≥200 mg/dL with hyperglycemia symptoms.
• B. Fasting plasma glucose ≥110 mg/dL
• C. HbA1c ≥5.7%
• D. Random plasma glucose ≥140 mg/dL

Answer: (A)

These thresholds reflect the different ways diabetes can be detected when glucose remains higher than normal across time or under stress. They are the standard diagnostic criteria because each test captures a different aspect of hyperglycemia.

• Fasting plasma glucose of 126 mg/dL (7.0 mmol/L) or higher means elevated glucose after an overnight fast, indicating persistent hyperglycemia. This value is used when a patient has not eaten for at least 8 hours.

• HbA1c of 6.5% or higher shows an elevated average blood glucose over the previous two to three months, reflecting long-term glucose exposure rather than a single reading.

• A 2-hour plasma glucose of 200 mg/dL (11.1 mmol/L) or higher on an oral glucose tolerance test (after consuming 75 g of glucose) indicates impaired glucose handling after a glucose load.

• A random plasma glucose of 200 mg/dL (11.1 mmol/L) or higher, in the presence of classic hyperglycemia symptoms (such as polyuria, polydipsia, or unintended weight loss), can diagnose diabetes because it reflects overt hyperglycemia at a random time.

The other options aren’t considered diagnostic thresholds: 110 mg/dL fasting is too low to define diabetes, HbA1c of 5.7% is in the prediabetes range, and 140 mg/dL random glucose is not diagnostic on its own.