Which test is used as a confirmatory test for primary hyperaldosteronism?

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

Answer: (A)

A key concept here is how aldosterone responds to blocking the renin–angiotensin system. In primary hyperaldosteronism, aldosterone secretion is autonomous and largely independent of angiotensin II. Giving captopril, which inhibits ACE and lowers angiotensin II, should cause normal physiology to suppress aldosterone. But when aldosterone production is autonomous, suppression is inadequate or absent, so a failure to suppress aldosterone after captopril confirms the diagnosis. This is why the captopril suppression test is used as a confirmatory test after an initial screen for primary hyperaldosteronism.

The other tests serve different purposes: ACTH stimulation tests adrenal reserve or pituitary-adrenal axis function, the insulin tolerance test assesses growth hormone and ACTH/cortisol responses under hypoglycemia, and the dexamethasone suppression test is used to evaluate for Cushing’s syndrome.