The most accurate diagnostic test for Zollinger-Ellison syndrome (ZES) is

-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 mEq/h or >5 mEq/h 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 U/kg) is given and gastrin levels are checked before and after injection. - An increase in serum gastrin of 200 pg/mL 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.