A 58-year-old patient presents with sudden thunderclap headache ('worst headache of life') with meningism and photophobia. CT brain is negative for blood. Lumbar puncture is performed at 12 hours post-symptom onset. The CSF finding MOST consistent with subarachnoid hemorrhage is:

• A Xanthochromia on spectrophotometry ✓
• B Elevated CSF protein only
• C Equal RBC count in tubes 1 and 4 (non-traumatic)
• D Elevated opening pressure >25 cm H2O

Explanation

When CT brain is negative for SAH (sensitivity 98% within 6 hours, falling to 85-90% at 12 hours), lumbar puncture is essential. Xanthochromia — yellow discoloration of CSF due to oxyhaemoglobin and bilirubin from red cell lysis — is the gold standard for confirming SAH on LP and is detected by visual inspection and/or spectrophotometry. Spectrophotometry is more sensitive than visual inspection and is required to identify bilirubin. Xanthochromia develops within 2-4 hours of SAH and persists for up to 2 weeks. Equal RBC in all tubes merely confirms blood is non-traumatic but must be accompanied by xanthochromia to confirm SAH. Elevated protein and opening pressure are non-specific.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.