A 42-year-old woman with resistant hypertension (BP 158/96 mmHg on maximum doses of amlodipine, ramipril, and hydrochlorothiazide) has serum potassium of 3.1 mEq/L and a CT abdomen showing a 1.8 cm right adrenal nodule. Plasma aldosterone concentration (PAC) is 42 ng/dL and plasma renin activity (PRA) is 0.2 ng/mL/hr. The aldosterone-to-renin ratio (ARR) is:
- A 210 ng/dL per ng/mL/hr, consistent with primary aldosteronism requiring adrenal vein sampling ✓
- B 8.4 ng/dL per ng/mL/hr, which rules out primary aldosteronism
- C 42 ng/dL per ng/mL/hr, which is borderline requiring renal artery Doppler
- D 0.2 ng/dL per ng/mL/hr, consistent with secondary aldosteronism
Explanation
ARR = PAC/PRA = 42/0.2 = 210 ng/dL per ng/mL/hr. A cut-off of ≥30 (and many centres use ≥20 or ≥40 depending on units and assay) is positive for primary aldosteronism. An ARR of 210 far exceeds any threshold, strongly suggesting primary aldosteronism. Given a confirmed biochemical diagnosis with a unilateral adrenal nodule, adrenal vein sampling (AVS) is recommended to lateralise aldosterone excess before surgical adrenalectomy, as the imaging nodule may be incidental. AVS determines whether the source is unilateral (surgical) or bilateral (medical, treated with spironolactone/eplerenone).
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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