In insulinoma, the expected lab pattern is insulin high, proinsulin high, C-peptide high, and B-hydroxybutyric acid low.

• A. Insulin high, proinsulin high, C-peptide high, B-hydroxybutyric acid low
• B. Insulin low, proinsulin low, C-peptide low, B-hydroxybutyric acid high
• C. Insulin high, proinsulin low, C-peptide high, B-hydroxybutyric acid high
• D. Insulin high, proinsulin high, C-peptide low, B-hydroxybutyric acid low

Answer: (A)

In insulinoma there is endogenous overproduction of insulin from the pancreatic beta cells, so insulin levels rise and so do the related secretory products like C-peptide and proinsulin. Because insulin is present in high amounts, it suppresses lipolysis and ketogenesis, leading to a low level of ketone bodies such as beta-hydroxybutyric acid. This combination—high insulin, high C-peptide, high proinsulin, and low beta-hydroxybutyrate—fits the pattern seen with endogenous hyperinsulinemia from an insulin-secreting tumor.

If insulin were high but C-peptide and proinsulin were not elevated, that would point toward exogenous insulin administration rather than an insulinoma. Conversely, abnormalities like low C-peptide or low proinsulin with high insulin would not align with endogenous insulin secretion.