<p><strong>STUDY OBJECTIVE: </strong>We determine the optimal correction factor for cerebrospinal fluid WBC counts in infants with traumatic lumbar punctures.</p>

<p><strong>METHODS: </strong>We performed a secondary analysis of a retrospective cohort of infants aged 60 days or younger and with a traumatic lumbar puncture (cerebrospinal fluid RBC count ≥10,000 cells/mm(3)) at 20 participating centers. Cerebrospinal fluid pleocytosis was defined as a cerebrospinal fluid WBC count greater than or equal to 20 cells/mm(3) for infants aged 28 days or younger and greater than or equal to 10 cells/mm(3) for infants aged 29 to 60 days; bacterial meningitis was defined as growth of pathogenic bacteria from cerebrospinal fluid culture. Using linear regression, we derived a cerebrospinal fluid WBC correction factor and compared the uncorrected with the corrected cerebrospinal fluid WBC count for the detection of bacterial meningitis.</p>

<p><strong>RESULTS: </strong>Of the eligible 20,319 lumbar punctures, 2,880 (14%) were traumatic, and 33 of these patients (1.1%) had bacterial meningitis. The derived cerebrospinal fluid RBCs:WBCs ratio was 877:1 (95% confidence interval [CI] 805 to 961:1). Compared with the uncorrected cerebrospinal fluid WBC count, the corrected one had lower sensitivity for bacterial meningitis (88% uncorrected versus 67% corrected; difference 21%; 95% CI 10% to 37%) but resulted in fewer infants with cerebrospinal fluid pleocytosis (78% uncorrected versus 33% corrected; difference 45%; 95% CI 43% to 47%). Cerebrospinal fluid WBC count correction resulted in the misclassification of 7 additional infants with bacterial meningitis, who were misclassified as not having cerebrospinal fluid pleocytosis; only 1 of these infants was older than 28 days.</p>

<p><strong>CONCLUSION: </strong>Correction of the cerebrospinal fluid WBC count substantially reduced the number of infants with cerebrospinal fluid pleocytosis while misclassifying only 1 infant with bacterial meningitis of those aged 29 to 60 days.</p>