[The nonserological diagnostic approach to infectious mononucleosis in an emergency service].

Patients with infectious mononucleosis often are seen in Emergency Services because the infection may produce tonsillitis resistant to antibiotic therapy. However, the diagnosis of choice is specific serology, which usually takes days or weeks before results become available. Detection of lymphocytosis in peripheral blood, heterophilic antibodies, and the characteristic mononuclear cells by means of specialized blood counters, together with the clinical signs, have improved the quality of diagnosis in emergency services (93% sensitivity and 97.2% specificity). We found that simple identification by optical microscopy of the lymphomonocytes typical of infectious mononucleosis in a drop of peripheral blood, together with the clinical findings, have a better diagnostic sensitivity (96. 5%) and specificity (99.1%) than any other method available in emergency services.