<prompt> A 35-year-old male presents with symptoms of palpitations, tremors, nervousness and headache. His father has a history of type 2 DM and mother has a history of some psychiatric illness. He has no chronic medical conditions and takes no medications. He appears anxious, sweaty and shaky. His fingerstick glucose is 45 mgdl. The patient as administered a bolus of 50 glucose which rapidly improves his symptoms. CECT abdomen shows a mass as follows. Which of the following is likely to be seen after overnight fasting?Serum insulin Serum pro-insulin C-peptide levels Normal Normal NormalSerum insulin Serum pro-insulin C-peptide levels Increased Increased IncreasedSerum insulin Serum pro-insulin C-peptide levels Increased Normal DecreasedSerum insulin Serum pro-insulin C-peptide levels Decreased Increased Increased  <response>: The patients symptoms consistent with hypoglycaemia which are reversed on administration of glucose, suggests a diagnosis of hypoglycaemia in a non-diabetic individual which could be because of a beta cell tumour or surreptitious use of insulin or sulfonylurea. The CT shows a pancreatic mass thereby ouring a diagnosis of beta cell tumour. After overnight fasting, insulin should be suppressed, but in case of a beta cell tumour, insulin, pro-insulin and C-peptide are all elevated. In case of surreptitious use of insulin, C-peptide levels are low and only insulin is elevated. Sulfonylureas would increase both insulin and pro-insulin and would require a plasma sulfonylurea testing for confirmation, however the mass on the CT ours a beta cell tumour. 