Diagnostic tests of hypoglycemia?

• A. Post-Absorptive- Tolbutamide tolerance; Post-Prandial- Mixed-meal tolerance; Hypoglycemic dip- 5 hour OGTT
• B. Fasting glucose test only
• C. Random glucose measurement
• D. HbA1c measurement

Answer: (A)

Diagnosing hypoglycemia requires dynamic, provocative testing to reveal how glucose and insulin respond under controlled conditions. Simply measuring a single glucose value or using long-term averages doesn’t uncover the underlying cause of recurrent lows. The combination of provocative tests shown in the best option provides a functional picture of how the body handles glucose in different situations.

The post-absorptive tolbutamide tolerance test uses a sulfonylurea-like stimulus to provoke insulin release after an overnight fast. If hypoglycemia occurs in this setting, it helps assess beta-cell responsiveness and can point toward secretagogue-related or endogenous hyperinsulinemic mechanisms as contributing causes.

The post-prandial mixed-meal tolerance test challenges the system with a standard meal, eliciting a physiological insulin and glucose response after feeding. This is useful for detecting reactive or postprandial hypoglycemia that can occur when insulin secretion is inappropriately high after a meal or when there are abnormal hormonal responses to food.

The hypoglycemic dip during a 5-hour oral glucose tolerance test extends observation beyond the usual 2-hour window to catch late or delayed hypoglycemia, which can occur in certain reactive hypoglycemia syndromes or after abnormal glucose absorption or metabolism. Together, these tests map how the body regulates glucose across fasting, fed, and extended post-ingestion states, which is essential for pinpointing the cause of hypoglycemia.

Fasting glucose alone doesn’t explain the cause of hypoglycemia, random glucose lacks consistency for diagnosis and timing, and HbA1c reflects long-term average glucose rather than acute hypoglycemic events.