Abstract
Objective: Extreme leukocytosis is often considered a warning sign of serious bacterial infection (SBI) in febrile children. However, its diagnostic value remains controversial, particularly in the post-vaccination era. This study aimed to evaluate whether extreme leukocytosis is associated with an increased risk of SBI compared with moderate leukocytosis in pediatric emergency patients.
Materials and Methods: This single-center, retrospective comparative study included children aged 1 month to 18 years who presented to a tertiary pediatric emergency department in Ankara, Türkiye, with a white blood cell (WBC) count ≥15.000/mm³. Patients were classified into moderate (15.000–24.999/mm³) and extreme (≥25.000/mm³) leukocytosis groups. SBI frequency, C-reactive protein (CRP) levels, and multivariable predictors of SBI were analyzed.
Results: A total of 955 patients were included (423 extreme, 532 moderate leukocytosis). SBI was identified in 26.0% of extreme and 22.7% of moderate leukocytosis patients (p=0.243). In multivariable analysis, extreme leukocytosis was not independently associated with SBI (OR 1.18, 95% CI 0.86–1.61, p=0.308), whereas CRP (OR 1.05, 95% CI 1.02–1.07, p=0.001) and fever (OR 2.21, 95% CI 1.54–3.16, p<0.001) were significant predictors. CRP showed moderate discriminatory ability (AUC 0.649), with improved performance in the extreme leukocytosis subgroup (AUC 0.705).
Conclusion: Extreme leukocytosis was not associated with increased SBI risk compared with moderate leukocytosis. CRP provided independent predictive value and may serve as a more useful biomarker for SBI risk stratification in pediatric emergency patients with leukocytosis.