Question

A patient presents with symptoms of hypoglycemia. Investigations reveal decreased blood glucose and increased insulin levels. A C-peptide assay shows a normal level of C-peptide. The most likely diagnosis is:

• A. Insulinoma
• B. Accidental sulfonylurea ingestion
• C. Accidental exogenous insulin administration
• D. Accidental metformin ingestion

Hint:

Outside insulin has no C-peptide, so insulin is high but C-peptide is not.

Answer 1

The Correct Option is C

Use C-peptide as a tracer for where the insulin came from. The pancreas releases insulin and C-peptide together in equal amounts, so anything the body itself makes carries C-peptide along with it. A drug vial of insulin does not.

The patient is hypoglycemic with a high insulin level, yet C-peptide is not elevated. That mismatch is the giveaway. If the insulin were coming from the patient's own pancreas, C-peptide would have to be high too. Because it is not, the extra insulin must have come from outside the body, pointing to exogenous insulin administration. That is the diagnosis.

Rule the rest out. An insulinoma would flood the blood with home-made insulin, so C-peptide would be clearly high, which contradicts the stem. Sulfonylureas squeeze the pancreas to release stored insulin, so both insulin and C-peptide rise together. Metformin works by reducing glucose output and improving sensitivity, not by raising insulin, and on its own it rarely causes low sugar.

High insulin without matching C-peptide means injected insulin.
\[\boxed{\text{Accidental exogenous insulin administration}}\]