Nucleotide metabolism: crystals in gout: practice question

A Biochemistry 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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Biochemistry · Nucleotide metabolism: crystals in gout

Sample item

Joint fluid from a swollen first metatarsophalangeal joint is examined under compensated polarised light. Which finding confirms gout?

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

The answer and the reasoning

C. Needle-shaped crystals with strong negative birefringence

Gout is confirmed by monosodium urate crystals, which are needle-shaped, appear yellow when parallel to the compensator axis, and are strongly negatively birefringent. Calcium pyrophosphate crystals of pseudogout are rhomboid and weakly positively birefringent.

Option by option

  • A. Hexagonal crystals with no birefringence

    Hexagonal crystals suggest cystine in urine and are not a feature of joint fluid in gout.

  • B. Coffin-lid crystals that are not birefringent

    Coffin-lid crystals describe triple phosphate in urine and are not found in joint fluid.

  • C. Needle-shaped crystals with strong negative birefringence (correct)

    Correct. Urate crystals are needle-shaped and strongly negatively birefringent.

  • D. Rhomboid crystals with weak positive birefringence

    This is the typical appearance of calcium pyrophosphate crystals in pseudogout.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is C, Needle-shaped crystals with strong negative birefringence. Gout is confirmed by monosodium urate crystals, which are needle-shaped, appear yellow when parallel to the compensator axis, and are strongly negatively birefringent.

Why is "Hexagonal crystals with no birefringence" not the answer?

Hexagonal crystals suggest cystine in urine and are not a feature of joint fluid in gout.

Why is "Coffin-lid crystals that are not birefringent" not the answer?

Coffin-lid crystals describe triple phosphate in urine and are not found in joint fluid.

Why is "Rhomboid crystals with weak positive birefringence" not the answer?

This is the typical appearance of calcium pyrophosphate crystals in pseudogout.

What concept does this question test?

It tests Nucleotide metabolism: crystals in gout in Biochemistry. Calcium pyrophosphate crystals of pseudogout are rhomboid and weakly positively birefringent.

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 Nucleotide metabolism: crystals in gout?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.