Parasitology: antimalarial toxicity: 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.

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Microbiology · Parasitology: antimalarial toxicity

Sample item

A man given primaquine for Plasmodium vivax develops dark urine, jaundice and pallor on day 3. His smear shows bite cells and Heinz bodies. What is the mechanism?

ADirect invasion of red cells by merozoitesBRed cell membrane defect causing spherocytosisCImmune complex deposition on red cellsDOxidant stress in G6PD-deficient red cells, with inadequate NADPH to regenerate glutathione

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

The answer and the reasoning

D. Oxidant stress in G6PD-deficient red cells, with inadequate NADPH to regenerate glutathione

Primaquine generates oxidant metabolites. Red cells deficient in G6PD cannot produce enough NADPH to maintain reduced glutathione, so haemoglobin denatures into Heinz bodies and macrophages remove bitten cells, causing haemolysis. G6PD status should be checked before primaquine or tafenoquine.

Option by option

A. Direct invasion of red cells by merozoites
Merozoite invasion is part of malaria itself, and haemolysis on day 3 of primaquine is drug induced.
B. Red cell membrane defect causing spherocytosis
Spherocytosis is a membrane disorder and does not produce Heinz bodies.
C. Immune complex deposition on red cells
Immune complexes cause type III reactions and are not behind Heinz bodies.
D. Oxidant stress in G6PD-deficient red cells, with inadequate NADPH to regenerate glutathione (correct)
Correct. Oxidant injury in G6PD deficiency explains Heinz bodies, bite cells and haemolysis.

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 Microbiology question

What is the answer to this Microbiology question?

The best answer is D, Oxidant stress in G6PD-deficient red cells, with inadequate NADPH to regenerate glutathione. Primaquine generates oxidant metabolites.

Why is "Direct invasion of red cells by merozoites" not the answer?

Merozoite invasion is part of malaria itself, and haemolysis on day 3 of primaquine is drug induced.

Why is "Red cell membrane defect causing spherocytosis" not the answer?

Spherocytosis is a membrane disorder and does not produce Heinz bodies.

Why is "Immune complex deposition on red cells" not the answer?

Immune complexes cause type III reactions and are not behind Heinz bodies.

What concept does this question test?

It tests Parasitology: antimalarial toxicity in Microbiology. Red cells deficient in G6PD cannot produce enough NADPH to maintain reduced glutathione, so haemoglobin denatures into Heinz bodies and macrophages remove bitten cells, causing haemolysis. G6PD status should be checked before primaquine or tafenoquine.

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 Parasitology: antimalarial toxicity?

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.