Immunology: c-ANCA and proteinase 3: 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 · Immunology: c-ANCA and proteinase 3

Sample item

A 42-year-old man has chronic sinusitis with nasal crusting, cough with haemoptysis and haematuria with red cell casts. Which autoantibody is most strongly associated with this picture?

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

The answer and the reasoning

C. Antibody to proteinase 3, giving a cytoplasmic ANCA pattern

Upper airway disease, lung involvement and necrotising glomerulonephritis define granulomatosis with polyangiitis, which is typically associated with anti-proteinase 3 antibodies and a cytoplasmic (c-ANCA) immunofluorescence pattern. Anti-myeloperoxidase (p-ANCA) is more typical of microscopic polyangiitis. Anti-GBM disease gives lung and kidney involvement without granulomatous upper airway disease.

Option by option

  • A. Antibody to myeloperoxidase, giving a perinuclear pattern

    Anti-myeloperoxidase gives a p-ANCA pattern and is more typical of microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis.

  • B. Antibody to double-stranded DNA

    Anti-dsDNA is a marker of lupus, which does not typically cause this granulomatous upper airway disease.

  • C. Antibody to proteinase 3, giving a cytoplasmic ANCA pattern (correct)

    Correct. Proteinase 3 antibodies give the c-ANCA pattern of granulomatosis with polyangiitis.

  • D. Antibody to glomerular basement membrane type IV collagen

    Anti-GBM antibodies cause Goodpasture disease, which spares the upper airways.

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 Microbiology question

What is the answer to this Microbiology question?

The best answer is C, Antibody to proteinase 3, giving a cytoplasmic ANCA pattern. Upper airway disease, lung involvement and necrotising glomerulonephritis define granulomatosis with polyangiitis, which is typically associated with anti-proteinase 3 antibodies and a cytoplasmic (c-ANCA) immunofluorescence pattern.

Why is "Antibody to myeloperoxidase, giving a perinuclear pattern" not the answer?

Anti-myeloperoxidase gives a p-ANCA pattern and is more typical of microscopic polyangiitis and eosinophilic granulomatosis with polyangiitis.

Why is "Antibody to double-stranded DNA" not the answer?

Anti-dsDNA is a marker of lupus, which does not typically cause this granulomatous upper airway disease.

Why is "Antibody to glomerular basement membrane type IV collagen" not the answer?

Anti-GBM antibodies cause Goodpasture disease, which spares the upper airways.

What concept does this question test?

It tests Immunology: c-ANCA and proteinase 3 in Microbiology. Anti-myeloperoxidase (p-ANCA) is more typical of microscopic polyangiitis. Anti-GBM disease gives lung and kidney involvement without granulomatous upper airway disease.

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 Immunology: c-ANCA and proteinase 3?

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.