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 mg/dl. 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?

The patient's 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.