Which statement best describes the diagnostic criterion for insulinoma/endogenous hyperinsulinism after fasting?

• A. Increase in plasma glucose by more than 25 mg/dL after fasting
• B. Change in plasma glucose > 25 mg/dL after fasting
• C. Decrease in plasma glucose by more than 25 mg/dL after fasting
• D. No change in plasma glucose after fasting

Answer: (B)

During a fasting test to evaluate endogenous hyperinsulinism, the important sign is how glucose behaves as the body is deprived of food. In a person with insulinoma, insulin continues to be released even as glucose falls, so the plasma glucose drops noticeably. A change in plasma glucose greater than 25 mg/dL after fasting captures this abnormal response—signaling that glucose is not being adequately maintained despite the fasting state. The direction of the change isn’t the point in this criterion; what matters is that there is a sizable, abnormal shift in glucose during the fast, which points toward autonomous insulin secretion.

An increase in glucose would not fit the pattern of endogenous hyperinsulinism, and no change would suggest a normal fasting response. While a decrease by more than 25 mg/dL describes the same phenomenon, stating the magnitude of change without specifying direction is the clinically recognized way to express the diagnostic threshold in this context.