A study of 200 fevers of unknown origin in nonhospitalized children showed that the value of the white blood cell and differential counts as predictors of cause is limited. In various viral infections, high neutrophil counts, even with numerous immature forms, were seen. An absolute neutrophil count below 5,000, however, was strong evidence against a bacterial cause.
Stein RC. The White Blood Cell Count in Fevers of Unknown Origin. Am J Dis Child. 1972;124(1):60-63. doi:10.1001/archpedi.1972.02110130062009