A 45-year-old man has hypertension, hypokalaemia, and metabolic alkalosis. Aldosterone-to-renin ratio (ARR) is 45 (ng/dL per ng/mL/h). Which confirmatory test has the highest specificity for primary hyperaldosteronism?

• A Salt loading test (IV sodium chloride 2 L over 4 hours; aldosterone <5 ng/dL = excluded)
• B Fludrocortisone suppression test (aldosterone >6 ng/dL on day 4 = confirmed) ✓
• C Captopril challenge test (failure to suppress aldosterone by >30%)
• D 24-hour urine aldosterone >14 µg on high-salt diet

Explanation

The fludrocortisone suppression test (FST) is considered the gold standard confirmatory test for primary hyperaldosteronism, with aldosterone levels greater than 6 ng/dL after 4 days of fludrocortisone 0.1 mg four times daily plus oral salt loading confirming the diagnosis. The IV saline loading test is more widely used due to convenience but has lower specificity. The captopril challenge has the lowest diagnostic accuracy among standard tests. The 24-hour urine test is used but less specific than the FST.

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

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Written and medically reviewed by the StethoPrep medical team.