Clinical biochemistry: xanthochromia in subarachnoid haemorrhage: 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 · Clinical biochemistry: xanthochromia in subarachnoid haemorrhage

Sample item

A man has a sudden severe headache and a normal CT scan of the head. Lumbar puncture 14 hours after onset gives CSF that is yellow after centrifugation. Which pigment formed in vivo from lysed red cells gives this colour and favours subarachnoid haemorrhage over a traumatic tap?

ABilirubinBUrobilinogenCMyoglobinDHaemosiderin in macrophages

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

The answer and the reasoning

A. Bilirubin

After subarachnoid bleeding, red cells in CSF lyse and haem is converted to bilirubin by haem oxygenase within the CNS, giving xanthochromia from about 12 hours. Because this occurs only in vivo, it is not produced by a traumatic tap. CSF spectrophotometry for bilirubin is used when CT is negative.

Option by option

A. Bilirubin (correct)
Correct. Bilirubin forms only in vivo from lysed red cells and gives the yellow supernatant.
B. Urobilinogen
Urobilinogen is formed in the gut from bilirubin and does not colour CSF.
C. Myoglobin
Myoglobin is a muscle pigment and is not found in CSF.
D. Haemosiderin in macrophages
Haemosiderin is stored in macrophages and does not colour the CSF supernatant.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is A, Bilirubin. After subarachnoid bleeding, red cells in CSF lyse and haem is converted to bilirubin by haem oxygenase within the CNS, giving xanthochromia from about 12 hours.

Why is "Urobilinogen" not the answer?

Urobilinogen is formed in the gut from bilirubin and does not colour CSF.

Why is "Myoglobin" not the answer?

Myoglobin is a muscle pigment and is not found in CSF.

Why is "Haemosiderin in macrophages" not the answer?

Haemosiderin is stored in macrophages and does not colour the CSF supernatant.

What concept does this question test?

It tests Clinical biochemistry: xanthochromia in subarachnoid haemorrhage in Biochemistry. Because this occurs only in vivo, it is not produced by a traumatic tap. CSF spectrophotometry for bilirubin is used when CT is negative.

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 Clinical biochemistry: xanthochromia in subarachnoid haemorrhage?

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.