This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Disorders of Adrenal Gland, Subject name: Medicine
A 35 year old male known case of MEN 1 presents to OPD with urinary stones and increased serum calcium. Next investigation to be done is? 
Select and explain. 
A. Urinary Metanephrine, B. Secretin study, C. Serum calcitonin levels, D. 72 hour prolonged fasting
B: Secretin study
Answer: B: Secretin study 
Explanation: Patient of MEN 1 have Pituitary adenoma Parathyroid adenoma-Most common and earliest manifestation is hyperparathyroidism with symptomatic hypercalcemia. Pancreatic adenoma (Gastrinoma>insulinoma) In diagnosed cases of MEN1 where nephrocalcinosis is documented, evaluation of pancreatic adenoma is impoant. The most common pancreatic adenoma in MEN 1 is ZES and hence for evaluation of ZES, secretin study is done. Subsequently 72 hours fasting test and endoscopic ultrasound will be useful for evaluation of insulinoma. The incidence of ZES in MEN I is 70% versus insulinoma being 10%. Surgical management is Definitive treatment of choice = If a MEN 2A patient has the same presentation, then calcitonin levels and urinary metanephrine levels shall be performed =In MEN IIA, incidence of medullary carcinoma thyroid (90%) is more than that of pheochromocytoma (20-35%).