Which test is used as a screening test for primary adrenal insufficiency?

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

Answer: (A)

The test used to screen for primary adrenal insufficiency is the ACTH stimulation (cosyntropin) test because it directly checks how well the adrenal cortex can produce cortisol when given ACTH. In a healthy person, administering synthetic ACTH should trigger a robust rise in cortisol within 30 to 60 minutes. If cortisol fails to rise above the expected threshold (typically around 18 μg/dL or 500 nmol/L after stimulation), this indicates the adrenal glands cannot respond, which points to primary adrenal insufficiency where the adrenal cortex is damaged or exhausted.

This test is preferred for screening because it directly assesses the functional capacity of the adrenal glands themselves, helping distinguish true adrenal failure from problems higher up in the HPA axis. Other tests serve different roles and aren’t used for routine screening of primary adrenal insufficiency: the metyrapone test evaluates ACTH reserve and the feedback system and is more of a specialized, slower diagnostic tool; the insulin tolerance test tests the entire hypothalamic–pituitary–adrenal axis but carries risks and is typically reserved for more detailed assessment; and the dexamethasone suppression test is used to evaluate hypercortisolism (Cushing syndrome), not adrenal insufficiency.