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SAH Xanthochromia — RACP Adult Medicine MCQ

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ModerateNeurologySAH XanthochromiaRACP Adult Medicine

A 35-year-old man presents with acute onset severe headache and neck stiffness. CT brain is performed 2 hours after symptom onset and is reported as normal. LP is performed 14 hours later. CSF shows uniformly blood-stained fluid in all 3 tubes. The supernatant is xanthochromic (yellow). What is the significance of xanthochromia?

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Correct answer: A — It is a normal finding

Xanthochromia (yellow discolouration of CSF supernatant due to bilirubin from haemoglobin degradation) in CSF collected ≥12 hours after headache onset is the gold standard for confirming subarachnoid haemorrhage when CT is negative. Bilirubin takes 6–12 hours to form from RBC lysis, distinguishing true SAH from a traumatic tap (which produces RBCs but no xanthochromia). Spectrophotometry is more sensitive than visual inspection. If SAH is confirmed, CT angiography is the next step to identify the source (aneurysm in 85%).

Reference: eTG – 2025 – Neurology; Stroke Foundation – 2024 – Clinical Guidelines