Toxicology: carbon monoxide: 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 · Toxicology: carbon monoxide

Sample item

Why can pulse oximetry be misleading in carbon monoxide poisoning?

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

The answer and the reasoning

A. It may read carboxyhemoglobin as oxyhemoglobin

Standard pulse oximeters cannot reliably distinguish oxyhemoglobin from carboxyhemoglobin, so saturation may appear falsely reassuring. Co-oximetry is needed for accurate carboxyhemoglobin measurement.

Option by option

  • A. It may read carboxyhemoglobin as oxyhemoglobin (correct)

    Correct. Optical overlap can create falsely high displayed saturation.

  • B. It measures carbon dioxide concentration directly

    Capnography, not pulse oximetry, estimates exhaled carbon dioxide.

  • C. It detects cyanide specifically

    Cyanide requires different diagnostic assessment.

  • D. It always reads zero during poisoning

    Readings are not necessarily zero.

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 A, It may read carboxyhemoglobin as oxyhemoglobin. Standard pulse oximeters cannot reliably distinguish oxyhemoglobin from carboxyhemoglobin, so saturation may appear falsely reassuring.

Why is "It measures carbon dioxide concentration directly" not the answer?

Capnography, not pulse oximetry, estimates exhaled carbon dioxide.

Why is "It detects cyanide specifically" not the answer?

Cyanide requires different diagnostic assessment.

Why is "It always reads zero during poisoning" not the answer?

Readings are not necessarily zero.

What concept does this question test?

It tests Toxicology: carbon monoxide in Forensic Medicine. Co-oximetry is needed for accurate carboxyhemoglobin measurement.

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 Toxicology: carbon monoxide?

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.