<prompt> Which of the following is the Gold standard diagnostic test for Insulinoma?72 hour fast testPlasma Glucose levels 3 mmolLPlasma Insulin levels 6 uUmlC- peptide levels 50 p molL  <response>: Gold standard test for the diagnosis of insulinoma is a supervised 72 hour fast test with measurement of serum glucose, C-peptide, proinsulin, and insulin every 4-8 hour. In non obese normal subjects, serum insulin levels should decrease to 6 UmL when blood glucose decreases to 40 mgdL and the ratio of insulin to glucose is 0.3 in mgdL. In a case of insulinoma, level of insulin increases 6 UmL when blood glucose is 40 mgdL. Other tests positive in insulinoma are an elevated C-peptide and serum proinsulin level, an insulinglucose ratio 0.3, and a decreased plasma-hydroxybutyrate level. Ref: Harrisons Internal Medicine, 18th Edition, Chapter 350 