Which test is used to confirm hypoglycemia in the diagnostic workup?

• A. 72-hour fasting with analysis of glucose, insulin, proinsulin, and C-peptide every 6 hours
• B. 2-hour oral glucose tolerance test
• C. Random glucose measurement during symptoms
• D. HbA1c testing

Answer: (A)

To confirm hypoglycemia in a diagnostic workup, you need biochemical documentation of a real low glucose level accompanied by inappropriately high insulin activity. The best way to provoke and study this is a supervised 72-hour fast. During this fast, blood glucose and related hormones are measured regularly—typically every 6 hours, and also at any time symptoms develop. You assess plasma glucose along with insulin, proinsulin, and C-peptide during the fast. The goal is to capture a hypoglycemic episode (glucose falls to a defined low level) and see whether insulin remains high or inappropriately present at that low glucose, while C-peptide is detectable, which points to endogenous insulin production. A negative sulfonylurea screen helps rule out ingestion of oral insulin secretagogues. This combination distinguishes endogenous hyperinsulinism (such as insulinoma) from other causes of low glucose.

Other tests aren’t suited for confirming hypoglycemia in this setting. The 2-hour oral glucose tolerance test is used to evaluate postprandial hyperglycemia, not endogenous hypoglycemia. Random glucose during symptoms may show low values but doesn’t provide the controlled, causal biochemical pattern needed. HbA1c reflects average blood glucose over months, not acute episodes of hypoglycemia.