A 52-year-old woman with type 2 diabetes on metformin and sitagliptin presents with recurrent hypoglycaemia and weight loss. Fasting insulin is markedly elevated; C-peptide is suppressed. Plasma proinsulin:insulin ratio is 0.2. Which diagnosis does this biochemical pattern confirm?
- A Insulinoma
- B Sulfonylurea abuse
- C Exogenous insulin administration ✓
- D Nesidioblastosis
Correct answer: C. Exogenous insulin administration
Explanation
Suppressed C-peptide with elevated insulin levels distinguishes exogenous insulin administration from endogenous hyperinsulinism. In insulinoma and sulfonylurea abuse, C-peptide is elevated (co-secreted with endogenous insulin). The normal or low proinsulin:insulin ratio also favours exogenous source as manufactured insulin contains no proinsulin. Nesidioblastosis also elevates C-peptide.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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