Management of Traumatic Lumbar Puncture with Elevated WCC and RBC
When interpreting a traumatic LP, subtract 1 WBC for every 700 RBCs in the CSF to correct for blood contamination, and if the corrected WBC count exceeds 10 times the predicted contamination, this strongly suggests true meningitis requiring treatment. 1
Standard Correction Approach
The 1:700 correction ratio (1 WBC subtracted per 700 RBCs) is the recommended standard for both adults and children. 1 This formula provides adequate correction in most clinical circumstances, though it serves as a guide rather than an absolute rule. 1
Alternative Correction Methods
For neonates specifically, the peripheral blood correction formula may offer superior accuracy: True CSF WBC = Actual CSF WBC - [(WBC in blood × RBC in CSF) / RBC in blood]. 1 However, studies in neonates demonstrate that adjustment of WBC counts does not improve diagnostic utility and can result in loss of sensitivity with only marginal gains in specificity. 2
The protein should also be corrected by subtracting 0.1 g/dL for every 100 RBCs present. 1
Critical Decision Thresholds
If the corrected WBC count exceeds 10 times the predicted contamination from blood, this is both sensitive (90%) and specific (97%) for true meningitis. 1, 3 In pediatric studies, 93% of children with bacterial meningitis had observed-to-predicted (O:P) WBC ratios >10, while only 3% of culture-negative patients exceeded this threshold. 4
An O:P ratio ≥1 occurred in 100% of children with bacterial meningitis versus only 32% without meningitis. 4 Conversely, a WBC:RBC ratio ≤1:100 (0.01) and an O:P ratio ≤0.01 had 100% specificity and positive predictive value for absence of disease. 5
Additional Diagnostic Parameters
Beyond WBC correction, several CSF parameters help distinguish true infection from traumatic contamination:
- CSF lactate >35 mg/dL strongly suggests bacterial meningitis with 93% sensitivity and 96% specificity. 1
- Low CSF:plasma glucose ratio and elevated protein favor bacterial or tuberculous meningitis over viral causes. 1
- Polymorphonuclear predominance occurred in 97% of bacterial meningitis cases versus 11% of culture-negative traumatic LPs. 4
- Hypoglycorrhachia was present in 73% of bacterial meningitis versus 3% of traumatic LPs without infection. 4
Distinguishing True Hemorrhage from Traumatic Tap
Serial bloody CSF specimens (tubes 1,2,3,4 all bloody) suggest true hemorrhage rather than procedural trauma. 1 In HSV encephalitis specifically, elevated RBC counts result from hemorrhagic pathophysiology, not traumatic tap—approximately 50% of HSV encephalitis cases have elevated CSF RBC counts due to the disease itself. 6
When to Repeat the LP
If initial CSF is normal but clinical suspicion remains high, repeat LP in 24-48 hours, particularly for suspected HSV encephalitis, which shows normal CSF in 5-10% of cases initially. 1, 7
Common Pitfalls to Avoid
Do not rely solely on mechanical application of correction formulas—integrate all clinical and laboratory data when deciding whether to treat. 3 In one study, 55% of traumatic LPs without meningitis had more WBCs than the ratio predicted, but only 10% exceeded 10 times the predicted value. 3
Traumatic LP occurred in 10.5% of procedures in thrombocytopenic patients but was not associated with adverse clinical outcomes. 6 The presence of blood contamination itself does not indicate harm or contraindicate interpretation.
Atraumatic needles reduce the likelihood of hemorrhagic LP for RBC counts ≤10 (OR 2.2-2.5 for non-hemorrhagic LP). 8
First-attempt LP success is associated with lower rates of hemorrhagic contamination (OR 2.8 for non-hemorrhagic LP). 8
Definitive Testing
CSF Gram stain, culture, and PCR testing (HSV-1/2, VZV, enterovirus) should guide definitive diagnosis regardless of traumatic contamination. 1, 7 Gram stain was positive in 80% of bacterial meningitis cases versus 0% of culture-negative traumatic LPs. 4