Following overnight fasting, hypoglycemia in adults is defined as a blood glucose level less than which value?

• A. <70 mg/dL (<3.9 mmol/L)
• B. <60 mg/dL (<3.3 mmol/L)
• C. <55 mg/dL (<3.0 mmol/L)
• D. <45 mg/dL (<2.5 mmol/L)

Answer: (D)

In this setting, the key idea is the threshold used by clinical chemistry to flag a clinically significant hypoglycemic event after an overnight fast. The cut-off chosen for defining hypoglycemia in adults under fasting conditions is 45 mg/dL, which is 2.5 mmol/L. Values at or below this level are considered sufficiently low to raise concern for potential neuroglycopenia and to prompt urgent clinical attention. Normal fasting glucose is typically about 70–99 mg/dL, so the stricter 45 mg/dL threshold is used to identify true, clinically important hypoglycemia rather than milder dips that may occur with variation or symptoms.