The purpose of this study was to identify useful predictors for diagnosing bacterial meningitis and performing CSF studies in febrile infants three months or younger.

Six hundred and fifty two febrile infants with a rectal temperature ≥38.0 ℃ presented from January 2003 to April 2008 and were retrospectively studied. The total white blood cell count (WBC), band count, absolute neutrophil count (ANC), quantitative C-reactive protein (CRP) and blood cultures were performed on admission. The clinical variables associated with bacterial meningitis were analyzed.

In patients with bacterial meningitis, the clinical variables including CRP (P= 0.036), band count (P=0.037), ANC (P=0.036) and age (P=0.001) were significantly different. The area under the receiver-operating characteristic curve was 0.969 for CRP, 0.946 for the band count, 0.765 for the ANC and 0.235 for age. A CRP cutoff point of 8 mg/dL was determined to maximize both the sensitivity and specificity (sensitivity 83%, specificity 95%, likelihood ratio 16.6). A CRP concentration of <7 mg/dL “ruled-out” bacterial meningitis, with a likelihood ratio of 0.17, a posttest probability of <0.1% and negative predictive value 91%. A CRP concentration greater than 9 mg/dL had a much higher likelihood ratio (20.1) than the band count (16.6) and ANC (2.2).

The CRP concentration was a useful laboratory test for the differential diagnosis of bacterial meningitis among febrile infants three months of age or younger. A CRP concentration of<7 mg/dL effectively ruled out bacterial meningitis; a value ≥9 mg/dL increased the clinical suspicion of bacterial meningitis and the need for CSF evaluation.