Identification: bloodstains and seminal fluid grouping: 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 · Identification: bloodstains and seminal fluid grouping

Sample item

In a rape case, a seminal stain on a sheet is grouped and shows group B antigen, yet the accused's blood group is O. The accused is a known secretor. What does this indicate?

AThe test is meaningless because semen never carries blood group antigensBThe stain is from the victim's menstrual bloodCThe accused must be non-secretorDThe semen did not come from the accused, since a secretor would show H substance only

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

The answer and the reasoning

D. The semen did not come from the accused, since a secretor would show H substance only

In secretors, ABO antigens appear in body fluids including semen and saliva. A group O secretor would show only H substance, so group B antigen excludes him as the source, provided contamination by the victim's fluids is excluded. Modern practice relies mainly on DNA profiling.

Option by option

A. The test is meaningless because semen never carries blood group antigens
About 80% of people secrete ABO antigens in body fluids, so semen can be grouped.
B. The stain is from the victim's menstrual blood
Menstrual blood is not a source of seminal group antigen in this scenario.
C. The accused must be non-secretor
The question states he is a secretor, and a non-secretor would show none.
D. The semen did not come from the accused, since a secretor would show H substance only (correct)
A group O secretor secretes H substance only, so B antigen excludes him.

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 D, The semen did not come from the accused, since a secretor would show H substance only. In secretors, ABO antigens appear in body fluids including semen and saliva.

Why is "The test is meaningless because semen never carries blood group antig…" not the answer?

About 80% of people secrete ABO antigens in body fluids, so semen can be grouped.

Why is "The stain is from the victim's menstrual blood" not the answer?

Menstrual blood is not a source of seminal group antigen in this scenario.

Why is "The accused must be non-secretor" not the answer?

The question states he is a secretor, and a non-secretor would show none.

What concept does this question test?

It tests Identification: bloodstains and seminal fluid grouping in Forensic Medicine. A group O secretor would show only H substance, so group B antigen excludes him as the source, provided contamination by the victim's fluids is excluded. Modern practice relies mainly on DNA profiling.

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 Identification: bloodstains and seminal fluid grouping?

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.