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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 Injuries: gunshot residue testing?

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.

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Injuries: gunshot residue testing MCQ (B11-FM1-7)

Q: What is the answer to this Forensic Medicine question?

The best answer is D, The test detects nitrates and nitrites, which also come from fertiliser, tobacco, cosmetics and urine, so false positives are common. The paraffin test detects nitrates and nitrites from burnt powder, but these occur in many common substances, so it is non-specific.

Q: What concept does this question test?

It tests Injuries: gunshot residue testing in Forensic Medicine. Modern methods such as atomic absorption spectrometry or SEM-EDX look for barium, antimony and lead particles, which are far more specific.

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Forensic Medicine · Injuries: gunshot residue testing

Sample item

Hand swabs from a man suspected of firing a country-made pistol are positive on the old dermal nitrate (paraffin) test. Why is this result alone unreliable?

AIt becomes positive only after the weapon has been fired more than twenty timesBThe test detects only lead, which is never produced when a firearm is dischargedCIt is valid only for rifled long weapons and not for pistolsDThe test detects nitrates and nitrites, which also come from fertiliser, tobacco, cosmetics and urine, so false positives are common

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

The answer and the reasoning

D. The test detects nitrates and nitrites, which also come from fertiliser, tobacco, cosmetics and urine, so false positives are common

The paraffin test detects nitrates and nitrites from burnt powder, but these occur in many common substances, so it is non-specific. Modern methods such as atomic absorption spectrometry or SEM-EDX look for barium, antimony and lead particles, which are far more specific.

Option by option

A. It becomes positive only after the weapon has been fired more than twenty times
The test has no requirement of a number of discharges.
B. The test detects only lead, which is never produced when a firearm is discharged
Lead is among the elements released on firing, though the test does not look for it.
C. It is valid only for rifled long weapons and not for pistols
The test is not restricted to rifled weapons; its problem is poor specificity.
D. The test detects nitrates and nitrites, which also come from fertiliser, tobacco, cosmetics and urine, so false positives are common (correct)
Correct. Common sources of nitrates give false positive results.

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.

Injuries: gunshot residue testing: practice question

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The answer and the reasoning

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