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PAH Clearance — FRCA Primary MCQ

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HardPhysiology - RenalPAH ClearanceFRCA Primary

Clearance of para-aminohippurate is used clinically to estimate which renal flow variable?

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Correct answer: A — Effective renal plasma flow estimated from high PAH extraction

The best answer is “Effective renal plasma flow estimated from high PAH extraction”. PAH is filtered and avidly secreted by the proximal tubule, so most PAH delivered to functioning renal plasma is removed in one pass. Its clearance therefore estimates effective renal plasma flow, not true renal plasma flow exactly because extraction is less than complete. Renal blood flow requires adjustment for haematocrit.

Reference: Royal College of Anaesthetists, Primary FRCA Syllabus 2021: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf