Lysis of RBC’s in the CSF leads to degradation of hemoglobin to bilirubin and this process begins 2-4 hours after such cell enter the subarachnoid space.
90% of patients with a subarachnoid hemorrhage have xanthochromia within 12 hours and it persists for 2-4 weeks.
Systemic elevations of serum bilirubin greater than 10 mg/dL and traumatic lumbar puncture with more than 100,000 RBC’s/mm3 can cause xanthochromia.