Which diagnostic test is used to evaluate suspected hypoglycemia by prolonged fasting?

Which diagnostic test is used to evaluate suspected hypoglycemia by prolonged fasting?

• A. 72-hour fast
• B. Oral glucose tolerance test
• C. Random glucose
• D. HbA1c

Answer: (A)

Prolonged fasting tests are designed to provoke hypoglycemia in individuals who might have fasting-related, insulin-mediated hypoglycemia, such as an insulinoma or disrupted glucose regulation. In a 72-hour fast, you monitor glucose levels over time while the person remains without food. If hypoglycemia develops, you measure insulin, C-peptide, proinsulin, beta-hydroxybutyrate, and screen for sulfonylureas. The pattern you see helps distinguish endogenous insulin production (high insulin with high C-peptide and low beta-hydroxybutyrate) from exogenous insulin use (high insulin with low C-peptide) or secretagogue ingestion. The test relies on the body's failure to maintain glucose during extended fasting, so it directly tests the body's fasting glucose homeostasis to identify the cause of hypoglycemia. The oral glucose tolerance test, on the other hand, assesses glucose handling after a glucose load to diagnose diabetes or impaired glucose tolerance, not to evaluate fasting hypoglycemia. A random glucose provides a single measurement and may miss intermittent hypoglycemia. HbA1c reflects average glucose over the past few months and does not identify acute or fasting hypoglycemia.

Prolonged fasting tests are designed to provoke hypoglycemia in individuals who might have fasting-related, insulin-mediated hypoglycemia, such as an insulinoma or disrupted glucose regulation. In a 72-hour fast, you monitor glucose levels over time while the person remains without food. If hypoglycemia develops, you measure insulin, C-peptide, proinsulin, beta-hydroxybutyrate, and screen for sulfonylureas. The pattern you see helps distinguish endogenous insulin production (high insulin with high C-peptide and low beta-hydroxybutyrate) from exogenous insulin use (high insulin with low C-peptide) or secretagogue ingestion. The test relies on the body's failure to maintain glucose during extended fasting, so it directly tests the body's fasting glucose homeostasis to identify the cause of hypoglycemia.

The oral glucose tolerance test, on the other hand, assesses glucose handling after a glucose load to diagnose diabetes or impaired glucose tolerance, not to evaluate fasting hypoglycemia. A random glucose provides a single measurement and may miss intermittent hypoglycemia. HbA1c reflects average glucose over the past few months and does not identify acute or fasting hypoglycemia.