Communicable diseases: HIV early infant diagnosis: practice question

A PSM 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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PSM · Communicable diseases: HIV early infant diagnosis

Sample item

A 6-week-old infant, born to a mother with HIV who received ART in pregnancy, is brought for early infant diagnosis under the national programme. Which test is appropriate?

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

The answer and the reasoning

A. HIV DNA PCR on dried blood spot

Maternal IgG crosses the placenta and persists in the infant up to 18 months, so antibody-based tests cannot distinguish infant infection from passive maternal antibodies. Early infant diagnosis uses a virological test, HIV DNA PCR, first at about 6 weeks of age. A positive result needs a confirmatory sample, and antibody testing is used from 18 months of age.

Option by option

  • A. HIV DNA PCR on dried blood spot (correct)

    Correct. Virological testing detects infant infection directly in this age.

  • B. Western blot

    Western blot is an antibody confirmatory assay and has the same problem with maternal antibodies.

  • C. ELISA for HIV antibody

    ELISA also measures antibody and cannot separate maternal from infant antibody before 18 months.

  • D. Rapid antibody test

    A rapid antibody test would detect passively transferred maternal antibodies and be positive in most exposed infants.

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 PSM question

What is the answer to this PSM question?

The best answer is A, HIV DNA PCR on dried blood spot. Maternal IgG crosses the placenta and persists in the infant up to 18 months, so antibody-based tests cannot distinguish infant infection from passive maternal antibodies.

Why is "Western blot" not the answer?

Western blot is an antibody confirmatory assay and has the same problem with maternal antibodies.

Why is "ELISA for HIV antibody" not the answer?

ELISA also measures antibody and cannot separate maternal from infant antibody before 18 months.

Why is "Rapid antibody test" not the answer?

A rapid antibody test would detect passively transferred maternal antibodies and be positive in most exposed infants.

What concept does this question test?

It tests Communicable diseases: HIV early infant diagnosis in PSM. Early infant diagnosis uses a virological test, HIV DNA PCR, first at about 6 weeks of age. A positive result needs a confirmatory sample, and antibody testing is used from 18 months of age.

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 Communicable diseases: HIV early infant diagnosis?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM 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.