Forensic serology: prostate-specific antigen: practice question

A Forensic Medicine 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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Forensic Medicine · Forensic serology: prostate-specific antigen

Sample item

A vaginal swab from an alleged sexual assault shows no spermatozoa on microscopy. The suspect is known to be azoospermic. Which test can still show that seminal fluid was deposited?

AExamination of the swab under Wood's lamp as conclusive proofBRepeated microscopy for motile spermCDetection of prostate-specific antigen (p30) in the swabDAcid phosphatase test alone as conclusive proof

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

The answer and the reasoning

C. Detection of prostate-specific antigen (p30) in the swab

Prostate-specific antigen (p30) is secreted by the prostate and is present in seminal plasma irrespective of sperm count, so it is positive in azoospermia and after vasectomy. It is much more specific for semen than acid phosphatase, which is also found in vaginal fluid, or fluorescence under UV light, which is non-specific.

Option by option

A. Examination of the swab under Wood's lamp as conclusive proof
Fluorescence is non-specific, as many other stains also fluoresce.
B. Repeated microscopy for motile sperm
No sperm can be found in azoospermia, so microscopy cannot help.
C. Detection of prostate-specific antigen (p30) in the swab (correct)
Correct. p30 is a semen-specific protein that does not depend on sperm.
D. Acid phosphatase test alone as conclusive proof
Acid phosphatase is only presumptive since vaginal secretions contain it.

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 Forensic Medicine question

What is the answer to this Forensic Medicine question?

The best answer is C, Detection of prostate-specific antigen (p30) in the swab. Prostate-specific antigen (p30) is secreted by the prostate and is present in seminal plasma irrespective of sperm count, so it is positive in azoospermia and after vasectomy.

Why is "Examination of the swab under Wood's lamp as conclusive proof" not the answer?

Fluorescence is non-specific, as many other stains also fluoresce.

Why is "Repeated microscopy for motile sperm" not the answer?

No sperm can be found in azoospermia, so microscopy cannot help.

Why is "Acid phosphatase test alone as conclusive proof" not the answer?

Acid phosphatase is only presumptive since vaginal secretions contain it.

What concept does this question test?

It tests Forensic serology: prostate-specific antigen in Forensic Medicine. It is much more specific for semen than acid phosphatase, which is also found in vaginal fluid, or fluorescence under UV light, which is non-specific.

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 Forensic serology: prostate-specific antigen?

Learn postmortem changes with their timelines, and toxicology as poison, sign, test and antidote. Then use the flashcards and the other Forensic Medicine 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.