Blood and immunity: chronic granulomatous disease: 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 · Blood and immunity: chronic granulomatous disease

Sample item

A boy has recurrent abscesses of the liver and lung caused by Staphylococcus aureus and Aspergillus. The nitroblue tetrazolium test fails to turn blue. Why are catalase-positive organisms especially dangerous in this condition?

AThey destroy their own hydrogen peroxide, which the phagocyte cannot supplyBThey suppress neutrophil production in the marrowCThey bind and neutralise complement C3bDThey block phagosome-lysosome fusion in the neutrophil

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

The answer and the reasoning

A. They destroy their own hydrogen peroxide, which the phagocyte cannot supply

In chronic granulomatous disease the phagocyte NADPH oxidase is defective, so it cannot make superoxide and hydrogen peroxide. Catalase-negative bacteria still supply their own peroxide for myeloperoxidase to use, but catalase-positive organisms break it down and escape killing.

Option by option

A. They destroy their own hydrogen peroxide, which the phagocyte cannot supply (correct)
Correct. Catalase removes bacterial peroxide, leaving no oxidant for killing.
B. They suppress neutrophil production in the marrow
Marrow suppression is not the cause, as neutrophil counts are normal.
C. They bind and neutralise complement C3b
C3b neutralisation is not the mechanism in this disorder.
D. They block phagosome-lysosome fusion in the neutrophil
Blocked phagolysosome fusion is the mechanism in Chediak-Higashi syndrome.

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 Physiology question

What is the answer to this Physiology question?

The best answer is A, They destroy their own hydrogen peroxide, which the phagocyte cannot supply. In chronic granulomatous disease the phagocyte NADPH oxidase is defective, so it cannot make superoxide and hydrogen peroxide.

Why is "They suppress neutrophil production in the marrow" not the answer?

Marrow suppression is not the cause, as neutrophil counts are normal.

Why is "They bind and neutralise complement C3b" not the answer?

C3b neutralisation is not the mechanism in this disorder.

Why is "They block phagosome-lysosome fusion in the neutrophil" not the answer?

Blocked phagolysosome fusion is the mechanism in Chediak-Higashi syndrome.

What concept does this question test?

It tests Blood and immunity: chronic granulomatous disease in Physiology. Catalase-negative bacteria still supply their own peroxide for myeloperoxidase to use, but catalase-positive organisms break it down and escape killing.

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 Blood and immunity: chronic granulomatous disease?

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.