Diagnosis of infectious mononucleosis.

Infectious mononucleosis continues to be an important medical problem of young adults. Diagnosis is based on three principal criteria: (1) a compatible clinical picture, (2) characteristic hematologic changes, and (3) a positive serology. A relative lymphocytosis of 60% or higher with at least 20% atypical lymphocytes is a common feature. Laboratory diagnosis is dependent on proper application and interpretation of the various serologic tests. Evidence of abnormal liver function is of particular value in differentiating this disease from bacterial and viral pharyngitis.