Which laboratory pattern suggests exogenous insulin administration as the cause of hypoglycemia?

• A. Increased insulin with decreased C-peptide.
• B. Increased insulin with increased C-peptide.
• C. Decreased insulin with decreased C-peptide.
• D. Normal insulin with normal C-peptide.

Answer: (A)

When hypoglycemia is due to external insulin, the body’s own insulin production is not driving the rise in insulin. C-peptide is released in equal amounts with endogenous insulin from the pancreas, so it serves as a marker of internal insulin production. Exogenous insulin raises circulating insulin levels but does not increase C-peptide, and endogenous secretion may be suppressed, leading to a high insulin level with a low C-peptide level. This pattern specifically points to injected insulin as the cause. In contrast, endogenous causes of high insulin (like insulinoma or sulfonylurea use) would show both insulin and C-peptide elevated, while non-hyperinsulinemic causes would not present with high insulin.