A 40-year-old woman with hypertension has unprovoked hypokalemia (K+ 3.0 mEq/L), metabolic alkalosis, and elevated 24-hour urine aldosterone despite suppressed plasma renin activity (PRA <0.1 ng/mL/hr). She is not on diuretics. CT adrenal glands show a right adrenal adenoma. What is the most important confirmatory test before deciding between surgery and medical therapy?

• A MRI adrenal with gadolinium
• B NP-59 (iodocholesterol) scintigraphy
• C Saline suppression test to confirm PA diagnosis
• D Adrenal vein sampling (AVS) to lateralize aldosterone excess ✓

Explanation

In primary aldosteronism (PA) with a unilateral adenoma on CT, adrenal vein sampling (AVS) is essential before surgery because CT imaging can miss contralateral microadenomas (~25% discordance with biochemistry) or bilateral hyperplasia mimicking a unilateral lesion. AVS determines whether aldosterone hypersecretion is truly unilateral (amenable to adrenalectomy) or bilateral (managed with mineralocorticoid receptor antagonists). The saline suppression test confirms PA diagnosis but is not needed at this stage. NP-59 scintigraphy has largely been replaced by AVS.

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

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Written and medically reviewed by the StethoPrep medical team.