In a patient with hypoglycemia showing increased insulin, proinsulin, and C-peptide levels, what could be the secondary cause?

The scenario presents a patient with hypoglycemia accompanied by increased levels of insulin, proinsulin, and C-peptide. In this context, the most likely secondary cause is surreptitious use of sulfonylureas.

Surreptitious use of sulfonylureas, which are medications that increase insulin secretion from the pancreas, leads to an increase in both insulin and C-peptide levels because these agents stimulate endogenous insulin production while also causing hypoglycemia. C-peptide is a byproduct of insulin synthesis, so elevated C-peptide levels indicate that the body is producing its own insulin in response to sulfonylurea administration.

In contrast, insulinoma is characterized by endogenous hyperinsulinemic hypoglycemia where high levels of insulin and C-peptide are produced by a tumor, but it is typically associated with fasting hypoglycemia rather than surreptitious medication use.

Thyroid storm can cause hypermetabolic states that might result in hypoglycemia but generally does not present with high insulin and C-peptide levels. Cushing syndrome can lead to increased glucose levels (hyperglycemia) and insulin resistance, rather than direct secretion of insulin leading to hypoglycemia.

Thus, the combination