INS and pancreatic insulinoma: Once Whipple's triad is confirmed, a supervised 72-hour fast is typically performed, considered the gold standard test for the diagnosis of insulinoma [15], which involves measuring the plasma glucose, insulin, C-peptide, and proinsulin levels every 6 hours until the plasma glucose reaches 60 mg/dL or lower, at which point the testing interval is reduced to every 1-2 hours.