Parasitology: malaria parasite density: practice question

A Microbiology 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.

Try it

Microbiology · Parasitology: malaria parasite density

Sample item

On a thick blood film from a febrile patient, 320 asexual malaria parasites are counted against 200 white blood cells. The patient's white cell count is 7500/µL. What is the parasite density?

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

The answer and the reasoning

A. 12,000 parasites/µL

Parasite density per microlitre equals parasites counted divided by white cells counted, multiplied by the white cell count per microlitre. Here 320 / 200 = 1.6, and 1.6 x 7500 = 12,000 parasites/µL. When a measured count is unavailable, an assumed count of 8000/µL is used.

Option by option

  • A. 12,000 parasites/µL (correct)

    320/200 x 7500 gives 12,000 parasites/µL.

  • B. 1,200 parasites/µL

    This is a factor of ten too low, from a decimal error in the calculation.

  • C. 2,400 parasites/µL

    This results from dividing by 1000 white cells, which was not the number counted.

  • D. 48,000 parasites/µL

    This results from dividing by 50 white cells, which was not the number counted.

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.

More Microbiology questions

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is A, 12,000 parasites/µL. Parasite density per microlitre equals parasites counted divided by white cells counted, multiplied by the white cell count per microlitre.

Why is "1,200 parasites/µL" not the answer?

This is a factor of ten too low, from a decimal error in the calculation.

Why is "2,400 parasites/µL" not the answer?

This results from dividing by 1000 white cells, which was not the number counted.

Why is "48,000 parasites/µL" not the answer?

This results from dividing by 50 white cells, which was not the number counted.

What concept does this question test?

It tests Parasitology: malaria parasite density in Microbiology. Here 320 / 200 = 1.6, and 1.6 x 7500 = 12,000 parasites/µL. When a measured count is unavailable, an assumed count of 8000/µL is used.

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 Parasitology: malaria parasite density?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology 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.