For secondary adrenal insufficiency, which stimulation test is used as a screening test?

• A. ACTH stimulation test
• B. Metyrapone stimulation test
• C. Insulin tolerance test
• D. Dexamethasone suppression test

Answer: (B)

Assessing the pituitary–adrenal axis reserve by blocking cortisol synthesis is what this test does. Metyrapone inhibits the enzyme that converts 11-deoxycortisol to cortisol, so cortisol levels fall. In a healthy axis, the pituitary responds by raising ACTH, which drives production of the adrenal steroid precursors, including 11-deoxycortisol, causing its levels to rise. If the pituitary cannot increase ACTH adequately—as in secondary adrenal insufficiency—the expected rise in 11-deoxycortisol doesn’t occur and cortisol remains low. This pattern makes the metyrapone test a useful screening tool for secondary adrenal insufficiency, because it directly probes the pituitary’s ability to respond to decreased cortisol.

Other tests have different roles: the ACTH stimulation test mainly evaluates adrenal responsiveness and is more confirmatory for adrenal insufficiency rather than screening pituitary function; the insulin tolerance test is a more invasive, riskier method to assess the entire HPA axis; the dexamethasone suppression test is used to evaluate cortisol excess (Cushing’s syndrome) rather than insufficiency.