This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
Best provocative test for diagnosis of Gastrinoma is: 
Select and explain. 
A. Ca++ infusion test, B. Secretin injection test, C. ACTH stimulation test, D. Steroid assay
B: Secretin injection test
Answer: B: Secretin injection test 
Explanation: 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.