A 48-year-old woman is evaluated for secondary hypertension. She has hypokalemia (K 2.9 mEq/L), metabolic alkalosis, and blood pressure of 168/104 mmHg on three antihypertensives including a diuretic-free regimen. Plasma aldosterone:renin ratio (ARR) is 45 (normal < 30) ng/dL per ng/mL/h. Which confirmatory test should be performed next?
- A Oral sodium loading test or saline infusion test to confirm non-suppressibility of aldosterone ✓
- B Proceed directly to adrenal vein sampling
- C CT abdomen to identify adrenal adenoma
- D 24-hour urine metanephrines to exclude pheochromocytoma
Explanation
An elevated ARR is a screening test for primary hyperaldosteronism (Conn's syndrome), but a positive screen must be confirmed by demonstrating autonomous (non-suppressible) aldosterone secretion. The oral sodium loading or saline infusion test is a standard confirmatory test: in normal subjects, high sodium load suppresses aldosterone; failure to suppress (urinary aldosterone > 12 µg/24h or post-infusion plasma aldosterone > 10 ng/dL) confirms autonomous hypersecretion. Adrenal vein sampling is the gold-standard for subtype differentiation (adenoma vs. bilateral hyperplasia) but is performed after biochemical confirmation, not before. CT adrenal is part of subtype workup but is not a confirmatory biochemical test. Metanephrines exclude pheochromocytoma, which causes hypertension without suppressed renin or hypokalemia as the predominant features.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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