INS and Hypoglycemia: Hypoglycemia and the absence of physiological insulin suppression is suspicious for an endogenous, insulin producing source.43 The endogenous hyperinsulinism can be diagnosed by low blood glucose levels (< 55 mg/dL (3.0 mmol/l)), high insulin (⩾ 3 μU/ml (⩾18 pmol/L)) and c-peptide levels (⩾ 0.6 ng/mL (0.2 nmol/L)) and proinsulin determination (⩾5.0 pmol/L).44,45 There should be an absence of sulfonylurea in the plasma and/or urine.44 When Whipple’s triad is detected, the gold standard for diagnosing insulinoma is the 72-h fasting test.