Communicable diseases: interpreting a malaria rapid test: practice question

A PSM 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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PSM · Communicable diseases: interpreting a malaria rapid test

Sample item

A man treated with artemisinin combination therapy for falciparum malaria 10 days earlier is afebrile, yet an HRP-2 based rapid test is positive at follow up. What is the best interpretation?

APersistent antigenaemia, to be confirmed by microscopy before calling it failureBDefinite treatment failure needing injectable artesunateCMixed infection with Plasmodium vivaxDLaboratory error as the test cannot detect falciparum antigen

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

The answer and the reasoning

A. Persistent antigenaemia, to be confirmed by microscopy before calling it failure

HRP-2 antigen can persist in blood for weeks after parasites are cleared, so a positive test in a recovered patient is not proof of failure. Microscopy should confirm the presence of parasites. Rapid tests based on HRP-2 are therefore unsuitable for monitoring treatment response.

Option by option

A. Persistent antigenaemia, to be confirmed by microscopy before calling it failure (correct)
Correct. HRP-2 persists after clearance and microscopy decides.
B. Definite treatment failure needing injectable artesunate
Failure cannot be diagnosed from antigen alone in an afebrile patient.
C. Mixed infection with Plasmodium vivax
HRP-2 is specific for falciparum, not vivax.
D. Laboratory error as the test cannot detect falciparum antigen
HRP-2 is the very antigen that detects falciparum malaria.

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.

Questions about this PSM question

What is the answer to this PSM question?

The best answer is A, Persistent antigenaemia, to be confirmed by microscopy before calling it failure. HRP-2 antigen can persist in blood for weeks after parasites are cleared, so a positive test in a recovered patient is not proof of failure.

Why is "Definite treatment failure needing injectable artesunate" not the answer?

Failure cannot be diagnosed from antigen alone in an afebrile patient.

Why is "Mixed infection with Plasmodium vivax" not the answer?

HRP-2 is specific for falciparum, not vivax.

Why is "Laboratory error as the test cannot detect falciparum antigen" not the answer?

HRP-2 is the very antigen that detects falciparum malaria.

What concept does this question test?

It tests Communicable diseases: interpreting a malaria rapid test in PSM. Microscopy should confirm the presence of parasites. Rapid tests based on HRP-2 are therefore unsuitable for monitoring treatment response.

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 Communicable diseases: interpreting a malaria rapid test?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM 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.