A 40-year-old man presents with hypertension, hypokalemia, and suppressed plasma renin activity. CT shows a 1.5 cm right adrenal adenoma. The biochemical hallmark confirming primary hyperaldosteronism is:

• A Elevated plasma cortisol with failed dexamethasone suppression
• B Elevated 24-hour urinary catecholamines and metanephrines
• C Elevated plasma ACTH with bilateral adrenal hyperplasia
• D Elevated aldosterone-to-renin ratio (ARR) with failure of aldosterone to suppress after salt loading ✓

Explanation

Primary hyperaldosteronism (Conn syndrome) is confirmed by an elevated aldosterone-to-renin ratio (screening) followed by confirmatory testing showing aldosterone autonomy—failure to suppress after oral or intravenous salt loading, which normally suppresses aldosterone in secondary causes. Suppressed plasma renin distinguishes primary from secondary hyperaldosteronism. Dexamethasone suppression is for Cushing syndrome; elevated catecholamines/metanephrines diagnose pheochromocytoma; elevated ACTH with bilateral hyperplasia suggests Cushing disease.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

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