A 35-year-old woman presents with episodes of obtundation, somnolence, and tachycardia. An insulinoma is suspected based on a random serum glucose test value of 38 mg. per dl. Which of the following statements is/are true?

D. An important component of the preoperative evaluation in patients with presumed insulinoma involves confirming elevated C-peptide or proinsulin levels and screening for anti-insulin antibodies.

 DISCUSSION: Insulinoma is the most common endocrine tumor of the pancreas. Insulinoma is associated with Whipple's triad, which consists of (1) symptoms of hypoglycemia at fasting; (2) documentation of blood glucose levels of less than 50 mg. per dl.; and (3) relief of symptoms following administration of glucose. The most reliable method for diagnosing insulinomas is a monitored fast. Neither an oral or an intravenous glucose tolerance test is indicated in the majority of patients being evaluated for insulinoma. Support for the diagnosis of insulinoma can come from documenting elevated C peptide and proinsulin levels. Screening for anti-insulin antibodies is indicated to rule out the possibility of surreptitious insulin administration. Tumor localization is typically performed with CT, endoscopic ultrasonography, or angiography. ERCP is not indicated for evaluation of most pancreatic endocrine tumors, as the tumors only rarely communicate with the main pancreatic duct system. As many as 90% of patients with insulinoma have benign solitary pancreatic adenomas amenable to surgical cure.