Environmental health: biochemical effect of lead: practice question

A PSM 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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PSM · Environmental health: biochemical effect of lead

Sample item

A battery-recycling worker has abdominal colic, constipation and a bluish line on the gums, and his blood film shows basophilic stippling. Lead interferes with haem synthesis. Which urinary abnormality is expected?

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

The answer and the reasoning

D. Raised delta-aminolevulinic acid

Lead inhibits delta-aminolevulinic acid dehydratase and ferrochelatase, so delta-aminolevulinic acid accumulates and is excreted in urine, along with coproporphyrin and raised zinc protoporphyrin in blood. Porphobilinogen is not typically increased, which distinguishes it from acute intermittent porphyria.

Option by option

  • A. Raised homogentisic acid

    Homogentisic acid accumulates in alkaptonuria and is unrelated to lead.

  • B. Raised 5-hydroxyindoleacetic acid

    5-hydroxyindoleacetic acid is raised in carcinoid syndrome, not in lead poisoning.

  • C. Raised porphobilinogen with normal delta-aminolevulinic acid

    A raised porphobilinogen with normal delta-aminolevulinic acid is not the pattern in lead poisoning.

  • D. Raised delta-aminolevulinic acid (correct)

    Correct. Inhibition of delta-aminolevulinic acid dehydratase raises urinary delta-aminolevulinic acid.

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 PSM question

What is the answer to this PSM question?

The best answer is D, Raised delta-aminolevulinic acid. Lead inhibits delta-aminolevulinic acid dehydratase and ferrochelatase, so delta-aminolevulinic acid accumulates and is excreted in urine, along with coproporphyrin and raised zinc protoporphyrin in blood.

Why is "Raised homogentisic acid" not the answer?

Homogentisic acid accumulates in alkaptonuria and is unrelated to lead.

Why is "Raised 5-hydroxyindoleacetic acid" not the answer?

5-hydroxyindoleacetic acid is raised in carcinoid syndrome, not in lead poisoning.

Why is "Raised porphobilinogen with normal delta-aminolevulinic acid" not the answer?

A raised porphobilinogen with normal delta-aminolevulinic acid is not the pattern in lead poisoning.

What concept does this question test?

It tests Environmental health: biochemical effect of lead in PSM. Porphobilinogen is not typically increased, which distinguishes it from acute intermittent porphyria.

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 Environmental health: biochemical effect of lead?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM 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.