Haematology: autoimmune haemolysis: practice question

A Pathology 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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Pathology · Haematology: autoimmune haemolysis

Sample item

A 22-year-old has jaundice and anaemia after a recent pneumonia with Mycoplasma. The direct Coombs test is positive for C3 only, and agglutination is seen on cooling the blood. Which antibody is responsible?

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

The answer and the reasoning

B. IgM cold agglutinin

Cold agglutinin disease is caused by IgM that binds red cells at low temperatures and fixes complement, giving a Coombs test positive for C3. It follows Mycoplasma infection and EBV.

Option by option

  • A. IgA anti-red cell antibody

    IgA antibodies are an uncommon cause of haemolysis.

  • B. IgM cold agglutinin (correct)

    Correct. IgM binds in the cold and a positive Coombs test for C3 only fits this.

  • C. IgG warm antibody

    Warm antibodies are IgG, and the Coombs test is positive for IgG with or without C3.

  • D. IgG Donath-Landsteiner antibody only

    Donath-Landsteiner antibody is biphasic IgG in paroxysmal cold haemoglobinuria after viral illness or syphilis.

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 Pathology question

What is the answer to this Pathology question?

The best answer is B, IgM cold agglutinin. Cold agglutinin disease is caused by IgM that binds red cells at low temperatures and fixes complement, giving a Coombs test positive for C3.

Why is "IgA anti-red cell antibody" not the answer?

IgA antibodies are an uncommon cause of haemolysis.

Why is "IgG warm antibody" not the answer?

Warm antibodies are IgG, and the Coombs test is positive for IgG with or without C3.

Why is "IgG Donath-Landsteiner antibody only" not the answer?

Donath-Landsteiner antibody is biphasic IgG in paroxysmal cold haemoglobinuria after viral illness or syphilis.

What concept does this question test?

It tests Haematology: autoimmune haemolysis in Pathology. It follows Mycoplasma infection and EBV.

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: autoimmune haemolysis?

Learn each disease as a bundle: cause, key histology, markers, and the clinical hallmark. Then use the flashcards and the other Pathology 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.