Lumbar puncture performed 12 hours after a sudden thunderclap headache shows xanthochromia of the supernatant after centrifugation. The pigment responsible and its source are:

• A Oxyhemoglobin released immediately from lysed red cells
• B Carotenoids diffusing from plasma across an intact barrier
• C Myoglobin released from adjacent muscle injury
• D Bilirubin formed from hemoglobin breakdown by macrophages in the CSF ✓

Explanation

After subarachnoid hemorrhage, lysed red cells release oxyhemoglobin, which macrophages convert to bilirubin over several hours. Bilirubin gives the yellow tint of xanthochromia detectable by spectrophotometry, and it persists for up to two weeks, making it more reliable than cell count for diagnosing hemorrhage days after onset. Oxyhemoglobin itself appears pinkish and is present early, myoglobin does not accumulate in CSF, and carotenoid diffusion is not the basis of pathological xanthochromia.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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