A RBC count exceeding 6,000/mm3 may indicate traumatic LP, but other important causes, mainly subarachnoid hemorrhage (SAH), should be ruled out. WBC elevation in traumatic LP is commonly explained by the blood leak if approximately one WBC is present per 750-1000 RBCs. The protein level is elevated in the presence of traumatic LP, and the glucose level is typically high.
Important findings that help to differentiate traumatic LP from SAH are xanthochromia and discoloration of centrifuged CSF due to hemoglobin breakdown. These are characteristic for SAH, and appear 2 to 4 hours after RBCs enter the subarachnoid space. These are present in more than 90% of patients within 12 hours of SAH.
Interestingly, in one study, a WBC/RBC ratio not exceeding 0.01 has almost 100% negative predictive value for meningitis.
| Xanthochromia | Absent |
|---|---|
| RBCs | 75,000/mm3 |
| WBCs | 100/mm3 |
| Protein | 50 mg/dL |
| Glucose | 90 mg/dL |
