GAST and gastrin-producing neuroendocrine tumor: The most commonly used provocative test for the diagnosis of gastrinomas involves the use of secretin (2 U/kg body weight) administered by intravenous bolus: Gastrin serum is measured baseline (at −15 and −1 min before the test) and then after 2, 5, 10, 15, 20, and 30 min following secretin administration.