Haematology: G6PD deficiency: practice question

A General Medicine 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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General Medicine · Haematology: G6PD deficiency

Sample item

A 26-year-old man develops dark urine, jaundice and pallor three days after starting primaquine for Plasmodium vivax malaria. Haemoglobin falls from 13 to 7.5 g/dL, the film shows bite cells and the direct Coombs test is negative. What is the underlying mechanism?

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

The answer and the reasoning

B. Reduced NADPH and glutathione, so red cells cannot withstand oxidant stress

G6PD deficiency is X-linked and impairs the pentose phosphate pathway, so red cells make too little NADPH to regenerate reduced glutathione. Oxidant drugs such as primaquine and dapsone, infection or fava beans denature haemoglobin into Heinz bodies, which the spleen removes as bite cells, causing intravascular and extravascular haemolysis. Testing before primaquine is advised.

Option by option

  • A. Absent CD55 and CD59 allowing complement-mediated lysis

    Loss of CD55 and CD59 causes paroxysmal nocturnal haemoglobinuria, which is not drug-triggered.

  • B. Reduced NADPH and glutathione, so red cells cannot withstand oxidant stress (correct)

    Correct. Without NADPH, red cells are defenceless against oxidant stress.

  • C. Defective spectrin in the red cell membrane skeleton

    A spectrin defect causes hereditary spherocytosis with spherocytes, not a drug-triggered episode.

  • D. Warm IgG antibody coating of red cells

    Warm autoimmune haemolysis would give a positive direct Coombs test.

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 General Medicine question

What is the answer to this General Medicine question?

The best answer is B, Reduced NADPH and glutathione, so red cells cannot withstand oxidant stress. G6PD deficiency is X-linked and impairs the pentose phosphate pathway, so red cells make too little NADPH to regenerate reduced glutathione.

Why is "Absent CD55 and CD59 allowing complement-mediated lysis" not the answer?

Loss of CD55 and CD59 causes paroxysmal nocturnal haemoglobinuria, which is not drug-triggered.

Why is "Defective spectrin in the red cell membrane skeleton" not the answer?

A spectrin defect causes hereditary spherocytosis with spherocytes, not a drug-triggered episode.

Why is "Warm IgG antibody coating of red cells" not the answer?

Warm autoimmune haemolysis would give a positive direct Coombs test.

What concept does this question test?

It tests Haematology: G6PD deficiency in General Medicine. Oxidant drugs such as primaquine and dapsone, infection or fava beans denature haemoglobin into Heinz bodies, which the spleen removes as bite cells, causing intravascular and extravascular haemolysis. Testing before primaquine is advised.

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 Haematology: G6PD deficiency?

For each disease know the classic presentation, the best test, and the first-line treatment. Then use the flashcards and the other General Medicine 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.