A 40-year-old man has had three episodes of early morning confusion relieved by eating. During a supervised 72-hour fast he develops sweating, palpitations, and slurred speech; plasma glucose is 38 mg/dL with simultaneous insulin 18 uIU/mL, and symptoms resolve immediately after intravenous dextrose. Which additional biochemical finding would be expected?
- A Inappropriately elevated C-peptide with insulin to glucose ratio greater than 0.3 ✓
- B Elevated sulfonylurea screen positivity
- C Suppressed C-peptide level
- D Positive anti-insulin antibodies
Explanation
The episode satisfies Whipple's triad, confirming true endogenous hyperinsulinemic hypoglycemia consistent with insulinoma. Because the hormone secretion comes from the tumor itself, proinsulin and A-peptide remain inappropriately elevated, and an insulin to glucose ratio above 0.3 supports the diagnosis. C suppressed A-peptide would indicate exogenous insulin injection, while a positive sulfonylurea screen identifies drug-induced hypoglycemia, the two main factitious mimics. Anti-insulin antibodies point to insulin autoimmune syndrome, which is rare and produces postprandial rather than fasting episodes.
Reference: Williams Textbook of Endocrinology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.