General physiology: indicator dilution: 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 · General physiology: indicator dilution

Sample item

To measure plasma volume, 15 mg of Evans blue dye is injected intravenously. After complete mixing the plasma concentration is 0.5 mg/dL. Ignoring any loss of dye from the circulation, what is the plasma volume?

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

The answer and the reasoning

B. 3 L

In the dilution principle volume = amount injected / concentration. Here 15 mg / 0.5 mg per dL = 30 dL, which is 3 L, a typical plasma volume. Evans blue binds albumin and stays in plasma, so it measures plasma volume; inulin or sucrose would be used for extracellular fluid.

Option by option

  • A. 0.75 L

    0.75 L results from multiplying 15 by 0.5 instead of dividing.

  • B. 3 L (correct)

    15 / 0.5 = 30 dL, and 10 dL make 1 L, so the volume is 3 L.

  • C. 14 L

    14 L approximates the extracellular fluid volume of a 70 kg adult, which needs a marker that leaves the vessels.

  • D. 30 L

    30 L results from forgetting that the answer of 30 is in decilitres, not litres.

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, 3 L. In the dilution principle volume = amount injected / concentration.

Why is "0.75 L" not the answer?

0.75 L results from multiplying 15 by 0.5 instead of dividing.

Why is "14 L" not the answer?

14 L approximates the extracellular fluid volume of a 70 kg adult, which needs a marker that leaves the vessels.

Why is "30 L" not the answer?

30 L results from forgetting that the answer of 30 is in decilitres, not litres.

What concept does this question test?

It tests General physiology: indicator dilution in Physiology. Here 15 mg / 0.5 mg per dL = 30 dL, which is 3 L, a typical plasma volume. Evans blue binds albumin and stays in plasma, so it measures plasma volume; inulin or sucrose would be used for extracellular fluid.

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 General physiology: indicator dilution?

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.