<prompt> Best provocative test for diagnosis of Gastrinoma is:Ca infusion testSecretin injection testACTH stimulation testSteroid assay  <response>: Answer is B Secretin injection test Gastrinomas Zollinger Ellison Syndrome are characterized by peptic ulceration due to hypersecretion of gastrin by a non-beta cell tumor. Secretin injection test is the most valuable provocative test in identifying patients with ZES. 