Diagnosing infectious mononucleosis: avoiding the pitfalls.

Infectious mononucleosis may be diagnosed with confidence only when Hoagland's diagnostic criteria have been met. The illness must be compatible with the known clinical features of infectious mononucleosis; there should be absolute and relative lymphocytosis on differential white cell count; there should be more than 20% atypical lymphocytes and serological tests should be positive-either a Paul-Bunnell Davidsohn or a rapid slide test for heterophil antibody. Failure to diagnose this common viral infection accurately may lead to inappropriate and perhaps harmful management, and may delay recognition of potentially life-threatening complications.