Which two markers are used to diagnose insulinoma?

• A. Proinsulin and C peptide
• B. Insulin and glucose
• C. HbA1c and glucose
• D. Glucagon and insulin

Answer: (A)

During hypoglycemia, an insulinoma causes inappropriately high insulin production from the pancreas. To tell that the insulin is coming from an endogenous source rather than from injected insulin, you look at markers that reflect the pancreas’s own secretion. Proinsulin and C-peptide rise along with insulin when the pancreas is autonomously producing insulin. If someone were injecting insulin, the insulin level would be high but C-peptide and proinsulin would stay low since there’s no corresponding pancreatic secretion. Thus, measuring proinsulin and C-peptide during a hypoglycemic episode most accurately identifies endogenous insulin production and supports a diagnosis of insulinoma. The other options don’t provide this distinction: insulin with glucose shows current levels but not the source; HbA1c with glucose reflects long-term control rather than acute hyperinsulinism; glucagon with insulin isn’t used to diagnose insulinoma.