This patient should undergo a 72-hour fast with hypoglycemic testing at the time of symptomatic hypoglycemia. He had symptomatic hypoglycemia with prolonged fasting (>5 hours) overnight that resolved with glucose administration. Since he is not currently hypoglycemic or symptomatic, fasting is necessary in an attempt to recreate the metabolic scenario that induced the hypoglycemia to allow definitive diagnosis. Glucose and hypoglycemic studies, including measurement of insulin, C-peptide, proinsulin, and β-hydroxybutyrate levels, should be obtained at the beginning of the fast and then repeated every 6 hours until the blood glucose level falls below 60 mg/dL (3.3 mmol/L), at which time they should be repeated every 1 to 2 hours until (1) symptomatic hypoglycemia (≤45 mg/dL [2.5 mmol/L]) occurs, (2) asymptomatic hypoglycemia (≤55 mg/dL [3.0 mmol/L]) occurs with previously documented Whipple triad, or (3) the 72-hour fast concludes. Whipple triad consists of three components: neuroglycopenia, concurrent hypoglycemia, and resolution of symptoms with correction of hypoglycemia.

Hypoglycemic studies are not adequately informative when the patient is not experiencing symptomatic hypoglycemia; therefore, testing now would not be appropriate.

Mixed-meal testing involves ingestion of a meal containing a mixture of protein, fat, and carbohydrates intended to raise the plasma blood glucose to assess the metabolic response to increased glucose. This test is appropriate when symptomatic hypoglycemia occurs within 5 hours after meal consumption (postprandial hypoglycemia). However, this patient's symptomatic hypoglycemia occurred 7 hours after his last meal; therefore, evaluation for postprandial hypoglycemia with a mixed-meal test would not be appropriate.

Oral glucose tolerance testing was previously used to evaluate postprandial hypoglycemia. However, it has not demonstrated effectiveness for this purpose and also would not be an appropriate study for evaluating fasting hypoglycemia.