Extreme white cell counts

Febrile children aged three months to three years with a white cell count over 25000/mm3 and fever were compared with controls whose leucoytosis was less extreme (15000-24999). The ‘extreme’ group had serious bacterial infection (SBI) in 39% compared with 15.4% controls. Pneumonia was the commonest SBI.
The authors conclude that 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. I conclude that leucocytosis is like fever: the cause may be benign, but the higher the number the less likely that is, even though the majority still won’t have SBI.
Extreme leucocytosis and the risk of serious bacterial infections in febrile children
Arch Dis Child. 2010 Mar;95(3):209-12