Abstract

Objective To determine the clinical significance of extreme leucocytosis (white blood cell (WBC) count >25 000/mm³) as a predictor of serious bacterial infection (SBI) in children.

Patients and methods A retrospective case–control study was conducted in a paediatric emergency department in Israel. The study evaluated children aged 3–36 months admitted to the emergency department with fever (>38°C) who had a complete blood count (CBC). Children with extreme leucocytosis were identified through the laboratory database. Further, for each case patient two consecutive febrile patients with WBC counts of 15 000–24 999/mm³ (moderate leucocytosis) served as controls (a case–control ratio of 1:2).

Results During the study, 146 patients with extreme leucocytosis were identified and compared with 292 patients with moderate leucocytosis. SBI was found in 57 (39%) patients with extreme leucocytosis compared with 45 (15.4%) control patients (p<0.001). The most commonly found SBI was segmental or lobar pneumonia, which was diagnosed in 41 (28%) patients in the case group compared with 27 (9.2%) patients in the control group (p<0.001, OR 3.83, 95% CI 2.25 to 6.52). Children with extreme leucocytosis were more often treated with antibiotics (52.7% vs 27.7%, p<0.001) and admitted to hospital (98.6% vs 50.68%, p<0.001).

Conclusions In febrile children aged 3–36 months, the presence of extreme leucocytosis is associated with a 39% risk of having SBIs. The increased risk for SBI is mainly due to a higher risk for pneumonia.