Gastrin, a major gastrointestinal hormone, serves to stimulate gastric acid secretion. Gastrin testing is helpful in the identification of Zollinger-Ellison tumors (gastrinomas) and other causes of hypergastrinemia. In fasting subjects, gastrin normally circulates at levels less than 100 pg/mL. A gastrin pH less than 5.0 and a serum gastrin greater than 1000 pg/mL are virtually diagnostic of ZES. Fasting gastrin levels greater than 500 pg/mL are consistent with patients with Zollinger-Ellison syndrome (ZES), but 40% of patients with ZES have values between 100-500 pg/mL and require a stimulation test for further assessment. Most patients with Zollinger-Ellison syndrome have serum gastrin concentrations between 150-1000 pg/mL (71-475 pmol/L). Hypergastrinemia may also present in patients with normal or slightly increased gastric acid secretion, including patients with achlorhydria (atrophric gastritis or pernicious anemia), renal insufficiency, massive small bowel resection, G-cell hyperplasia, gastric outlet obstruction, and retained gastric antrum, as well as in patients receiving potent antisecretory drugs. The differentiation between Zollinger-Ellison syndrome and patients with hypergastrinemia without gastrinoma can be aided by “provocative” tests (e.g. secretion challenge or calcium infusion test). In the secretion challenge test, greater than 95% of gastrinoma patients respond to secretin infusion with a significant elevation of gastrin levels above basal levels (a rise of at least 200 pg/mL).

Secretin Stimulation Test for Diagnosis of Gastrinoma (Zollinger-Ellison Syndrome)