A 48-year-old woman with resistant hypertension (BP 162/104 mmHg on three antihypertensives including a diuretic at optimal doses) has confirmed medication adherence. Aldosterone-renin ratio is elevated at 42 (ng/dL)/(ng/mL/hr). CT adrenals show bilateral normal adrenals. What is the next diagnostic step?

• A Start spironolactone empirically without further workup
• B Repeat aldosterone-renin ratio after stopping all antihypertensives
• C 24-hour urine aldosterone measurement
• D Adrenal vein sampling (AVS) to lateralise aldosterone source ✓

Explanation

Primary aldosteronism with an elevated ARR requires confirmation and then subtype differentiation. When CT adrenals are normal or inconclusive (bilateral normal appearance does not exclude unilateral adenoma — up to 40% of adenomas are < 1 cm), adrenal vein sampling (AVS) is the gold-standard test to lateralise aldosterone production and distinguish unilateral adenoma (surgical, adrenalectomy) from bilateral adrenal hyperplasia (medical, MRA therapy). Per Endocrine Society 2016 guidelines, AVS is required before surgery in all PA patients except those with obvious unilateral macroadenoma and age < 35. Starting MRA empirically would be appropriate for bilateral hyperplasia but must be confirmed.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.