Question category: Endocrinology
A 19 year old female presents with recurrent episodes of sweating, palpitations, dizziness and weakness. These episodes can occur at any time of the day but she has noticed them particularly at night. Her mother has type 1 diabetes mellitus. You admit her for a 48 hour fasting glucose. 12 hours after admission her glucose is noted to be 2.8 mmol/L and her insulin levels are greatly elevated. Which of the following investigation should be performed to confirm the diagnosis?