Immunopathology: p24 antigen in HIV testing: 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 · Immunopathology: p24 antigen in HIV testing

Sample item

A man presents 3 weeks after a high-risk exposure with fever, sore throat and a maculopapular rash. A rapid antibody-only test is negative. A fourth-generation assay detects antibody together with which viral antigen to shorten the window period?

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

The answer and the reasoning

D. p24 capsid antigen

Fourth-generation assays detect both HIV antibodies and p24 antigen. p24 is the core protein, and it appears in blood before antibodies in acute infection, which makes earlier diagnosis possible. It later falls as antibodies form complexes with it.

Option by option

  • A. gp120 envelope antigen

    gp120 is an envelope glycoprotein but is not the antigen targeted in the screening assay.

  • B. Reverse transcriptase

    Reverse transcriptase is an enzyme and not the assay target.

  • C. gp41 antibody

    gp41 antibodies are part of the late antibody response, not an antigen.

  • D. p24 capsid antigen (correct)

    Correct. p24 is the capsid protein that becomes detectable before seroconversion.

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 D, p24 capsid antigen. Fourth-generation assays detect both HIV antibodies and p24 antigen.

Why is "gp120 envelope antigen" not the answer?

gp120 is an envelope glycoprotein but is not the antigen targeted in the screening assay.

Why is "Reverse transcriptase" not the answer?

Reverse transcriptase is an enzyme and not the assay target.

Why is "gp41 antibody" not the answer?

gp41 antibodies are part of the late antibody response, not an antigen.

What concept does this question test?

It tests Immunopathology: p24 antigen in HIV testing in Pathology. p24 is the core protein, and it appears in blood before antibodies in acute infection, which makes earlier diagnosis possible. It later falls as antibodies form complexes with it.

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 Immunopathology: p24 antigen in HIV testing?

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.