Atypical lymphocytosis in children.

A complete blood count performed during the evaluation of a febrile or traumatized child may show the presence of atypical lymphocytosis. Although atypical lymphocytes occur in several conditions, they are most closely associated with infectious mononucleosis (IM). We initiated a study to determine if the presence in children of atypical lymphocytosis without the triad of splenomegaly, pharyngitis, and adenopathy is a manifestation of IM. Heterophil antibody (HA) and Epstein-Barr virus (EBV) titers were performed on 45 children with greater than or equal to 5% atypical lymphocytes. None had a significant HA titer. Thirty-three were seronegative for EBV, and 11 had titers indicative of past infection. One child had an antibody pattern suggesting a recent EBV infection; none had a titer consistent with acute IM. We conclude that isolated atypical lymphocytes does not point to infectious mononucleosis.