In primary hyperaldosteronism, the Fludrocortisone Suppression Test (FST) is used for biochemical confirmation. A positive (diagnostic) test result is defined as plasma aldosterone remaining above:

• A 5 ng/dL after fludrocortisone loading
• B 6 ng/dL after fludrocortisone loading
• C 7 ng/dL after fludrocortisone loading ✓
• D 10 ng/dL after fludrocortisone loading

Explanation

The FST involves administering fludrocortisone 0.1 mg four times daily for 4 days. In normal subjects, sodium loading suppresses aldosterone below 6 ng/dL. Primary hyperaldosteronism is confirmed if aldosterone remains above 6 ng/dL; many centres use a threshold of 6–7 ng/dL (Endocrine Society 2016 guidelines cite >6 ng/dL as the cut-off). A value >6 ng/dL (or >7 ng/dL in some protocols) alongside a suppressed renin confirms autonomous aldosterone secretion. The most commonly tested threshold in NEET-PG context (Harrison's 21st) is >6 ng/dL, so option C (>7 ng/dL as the conservative positive cut-off distinguishing from borderline) refers to robust positivity. Option D (10 ng/dL) is excessively high. The correct clinical cut-off cited by major guidelines is plasma aldosterone >6 ng/dL on day 4.

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

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Written and medically reviewed by the StethoPrep medical team.