Approach to hypoglycemia Quiz: Ace Your Exams

A 27-year-old man is admitted to the hospital following recurrent episodes of hypoglycemia. The patient has had several visits to the emergency department for hypoglycemia, which has been corrected in the ED with IV glucose administration. The patient has no past medical history and does not take any medications. The patient does not use alcohol, smoke cigarettes, or use other recreational drugs. Vital signs are within normal limits except for mild tachycardia. Physical examination is unremarkable. The patient's initial blood glucose upon arrival is 35 mg/dL, which is corrected to 80 mg/dL following administration of IV glucose. Bloodwork reveals an insulin level of 20 μU/mL, C-peptide level of 1.2 ng/mL, proinsulin level of 8 pmol/L, and β-hydroxybutyrate level < 2.7 mg/dL, and a negative screen for oral hypoglycemic agents. Which of the following tests should be performed next?