A low peripheral blood white blood cell count in infants younger than 90 days increases the odds of acute bacterial meningitis relative to bacteremia.

UNLABELLED: In relying on the peripheral blood white blood cell (WBC) count to identify infants at high risk for acute bacterial meningitis and bacteremia, to the best of the authors' knowledge, it has not been reported previously whether high and low values of the test have similar implications for predicting these separate infections.
OBJECTIVE: To analyze the relationship between the peripheral WBC count and the odds of acute bacterial meningitis relative to bacteremia among sick infants aged 3 to 89 days.
METHODS: Areas under the receiver operating characteristic curve (AUCs) and likelihood ratios at various intervals of the total peripheral blood WBC count were computed.
RESULTS: A pathogen was isolated from blood or cerebrospinal fluid (CSF) from 72 infants aged 3 to 89 days. Fifty-two infants had growth of a pathogen from the blood only, and 20 had growth from the CSF. The most common bacteria isolated were Escherichia coli (32) and group B streptococci (32). The AUC for the peripheral WBC count when differentiating between acute bacterial meningitis and bacteremia was 0.75 (95% CI = 0.63 to 0.88). The odds of acute bacterial meningitis relative to bacteremia were sevenfold higher for a peripheral WBC cutoff below 5,000 cells/mm(3) and threefold lower for a peripheral WBC cutoff at or above 15,000 cells/mm(3).
CONCLUSIONS: In young infants, the peripheral blood WBC count is useful for estimating the odds of acute bacterial meningitis relative to isolated bacteremia. A low peripheral blood WBC count should be considered a much more worrisome laboratory finding because it is associated with a relatively high risk for acute bacterial meningitis relative to the potential for bacteremia.