This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Medicine
Gold standard investigation for diagnosis of insulinoma - 
Select and explain. 
A. Blood glucose level less than 30 mg%, B. 72 hrs fasting, C. C peptide levels less than 32 rjm, D. Serum insulin levels
B: 72 hrs fasting
Answer: B: 72 hrs fasting 
Explanation: Pathology of pancreatic endocrine tumor (insulinoma). Specialty. Oncology. An insulinoma is a tumor of the pancreas that is derived from beta cells and secretes insulin. It is a rare form of a neuroendocrine tumor The diagnosis of insulinoma is suspected in a patient with symptomatic fasting hypoglycemia. The conditions of Whipple's triad need to be met for the diagnosis of "true hypoglycemia" to be made: symptoms and signs of hypoglycemia, concomitant p 72 hrs fasting blood glucose level of 45 mg/dL (2.5 mmol/L) or less, and reversibility of symptoms with administration of glucose. Ref Davidson edition23rd pg834