Renal: renal blood flow and filtration fraction: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Renal: renal blood flow and filtration fraction

Sample item

A man has para-aminohippurate clearance of 600 mL/min, inulin clearance of 120 mL/min and haematocrit 40%. What are his filtration fraction and renal blood flow?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Filtration fraction 0.20; renal blood flow 1000 mL/min

PAH clearance estimates effective renal plasma flow (600 mL/min) and inulin clearance estimates GFR (120 mL/min). Filtration fraction = GFR / RPF = 120 / 600 = 0.20. Renal blood flow = RPF / (1 - haematocrit) = 600 / 0.6 = 1000 mL/min.

Option by option

  • A. Filtration fraction 0.12; renal blood flow 1000 mL/min

    0.12 comes from dividing GFR by blood flow instead of plasma flow.

  • B. Filtration fraction 0.20; renal blood flow 1000 mL/min (correct)

    Correct. 120/600 gives 0.20 and 600/0.6 gives 1000 mL/min.

  • C. Filtration fraction 0.20; renal blood flow 600 mL/min

    600 mL/min is the plasma flow, and blood flow must include the red cell fraction.

  • D. Filtration fraction 0.20; renal blood flow 1500 mL/min

    1500 mL/min arises from dividing by the haematocrit (0.4) instead of one minus the haematocrit.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is B, Filtration fraction 0.20; renal blood flow 1000 mL/min. PAH clearance estimates effective renal plasma flow (600 mL/min) and inulin clearance estimates GFR (120 mL/min).

Why is "Filtration fraction 0.12; renal blood flow 1000 mL/min" not the answer?

0.12 comes from dividing GFR by blood flow instead of plasma flow.

Why is "Filtration fraction 0.20; renal blood flow 600 mL/min" not the answer?

600 mL/min is the plasma flow, and blood flow must include the red cell fraction.

Why is "Filtration fraction 0.20; renal blood flow 1500 mL/min" not the answer?

1500 mL/min arises from dividing by the haematocrit (0.4) instead of one minus the haematocrit.

What concept does this question test?

It tests Renal: renal blood flow and filtration fraction in Physiology. Filtration fraction = GFR / RPF = 120 / 600 = 0.20. Renal blood flow = RPF / (1 - haematocrit) = 600 / 0.6 = 1000 mL/min.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Renal: renal blood flow and filtration fraction?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.