Renal Blood Flow — FRCA Primary MCQ

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HardPhysiology - RenalRenal Blood FlowFRCA Primary

Cardiac output is 5.0 L/min and renal blood flow is 20% of cardiac output. If haematocrit is 0.40, which renal plasma flow is closest?

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Reveal the answer and explanation

Correct answer: C — 600 mL/min

The best answer is “600 mL/min”. Renal blood flow is 0.20 × 5.0 L/min = 1.0 L/min. Renal plasma flow equals blood flow × (1 − haematocrit), so 1000 × 0.60 = 600 mL/min. Values around 1000 mL/min confuse plasma flow with blood flow, whereas higher values cannot result from subtracting the red-cell fraction.

Reference: RCoA, Primary FRCA syllabus: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf; Measurement of renal function in chronic kidney disease: https://pmc.ncbi.nlm.nih.gov/articles/PMC3791974/