Renal: renal blood flow: 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

Sample item

In a healthy adult the clearance of para-aminohippurate (PAH) is 600 mL/min and the haematocrit is 40%. What is the approximate renal blood flow?

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

The answer and the reasoning

B. 1000 mL/min

PAH is filtered and almost completely secreted, so its clearance approximates effective renal plasma flow. Renal blood flow equals plasma flow divided by (1 minus haematocrit): 600 / 0.6 = 1000 mL/min. This is about 20% of cardiac output.

Option by option

  • A. 240 mL/min

    This multiplies by the haematocrit and gives the red cell flow, not total blood flow.

  • B. 1000 mL/min (correct)

    Correct. 600 / (1 - 0.4) = 1000 mL/min.

  • C. 600 mL/min

    This is the plasma flow, which excludes the cell volume of blood.

  • D. 1500 mL/min

    This divides by the haematocrit (600 / 0.4) instead of by the plasma fraction.

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, 1000 mL/min. PAH is filtered and almost completely secreted, so its clearance approximates effective renal plasma flow.

Why is "240 mL/min" not the answer?

This multiplies by the haematocrit and gives the red cell flow, not total blood flow.

Why is "600 mL/min" not the answer?

This is the plasma flow, which excludes the cell volume of blood.

Why is "1500 mL/min" not the answer?

This divides by the haematocrit (600 / 0.4) instead of by the plasma fraction.

What concept does this question test?

It tests Renal: renal blood flow in Physiology. Renal blood flow equals plasma flow divided by (1 minus haematocrit): 600 / 0.6 = 1000 mL/min. This is about 20% of cardiac output.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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?

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.