<prompt> The most accurate diagnostic test for Zollinger-Ellison syndrome ZES isFasting serum gastrinComputed tomography CT scanEndoscopySecretin stimulation test  <response>: -All patients with gastrinoma have an elevated gastrin level, and hypergastrinemia in the presence of elevated basal acid output BAO strongly suggests gastrinoma. -Patients with gastrinoma usually have a BAO 15 mEqh or 5 mEqh if they have had a previous procedure for peptic ulcer. -Acid secretory medications should be held for several days before gastrin measurement, because acid suppression may falsely elevate gastrin levels. 1. The diagnosis of Zollinger-Ellison syndrome ZES is confirmed by the secretin stimulation test. An intravenous IV bolus of secretin 2 Ukg is given and gastrin levels are checked before and after injection. - An increase in serum gastrin of 200 pgmL or greater suggests the presence of gastrinoma. Patients with gastrinoma should have serum calcium and parathyroid hormone levels determined to rule out multiple endocrine neoplasia type 1 MEN1 and, if present, parathyroidectomy should be considered before resection of gastrinoma. 