Sexual offences and forensic psychiatry: sperm staining: 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 · Sexual offences and forensic psychiatry: sperm staining

Sample item

A smear from a vaginal swab is stained to identify spermatozoa, using a stain that colours the head red and the tail green. What is this stain called?

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

The answer and the reasoning

D. Christmas tree stain

The Christmas tree stain uses nuclear fast red and picroindigocarmine, colouring the sperm head and acrosome red and pink and the tail green. It is simple and useful for finding sperm in smears. Gram, Giemsa and Ziehl-Neelsen stains are for microbes and blood cells.

Option by option

  • A. Ziehl-Neelsen stain

    Ziehl-Neelsen stain demonstrates acid-fast bacilli.

  • B. Giemsa stain

    Giemsa stain is used for blood and parasites.

  • C. Gram stain

    Gram stain differentiates bacteria and does not give a red head and green tail.

  • D. Christmas tree stain (correct)

    Correct. Nuclear fast red with picroindigocarmine gives the Christmas tree stain for sperm.

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 Forensic Medicine question

What is the answer to this Forensic Medicine question?

The best answer is D, Christmas tree stain. The Christmas tree stain uses nuclear fast red and picroindigocarmine, colouring the sperm head and acrosome red and pink and the tail green.

Why is "Ziehl-Neelsen stain" not the answer?

Ziehl-Neelsen stain demonstrates acid-fast bacilli.

Why is "Giemsa stain" not the answer?

Giemsa stain is used for blood and parasites.

Why is "Gram stain" not the answer?

Gram stain differentiates bacteria and does not give a red head and green tail.

What concept does this question test?

It tests Sexual offences and forensic psychiatry: sperm staining in Forensic Medicine. It is simple and useful for finding sperm in smears. Gram, Giemsa and Ziehl-Neelsen stains are for microbes and blood cells.

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 Sexual offences and forensic psychiatry: sperm staining?

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.