Infectious mononucleosis (IM) screen

IM is an acute herpes virus infection caused by the Epstein Barr Virus (EBV). It is a disease of variable severity, characterised by a range of symptoms that can include fever, lethargy, sore throat, lymphadenopathy, splenomegaly, hepatitis and jaundice. During the acute phase of illness, IM heterophile antibodies (primarily of the IgM class) appear in 80-90 % of IM cases. IM heterophile antibodies are usually demonstrable 1-12 weeks after the onset of the illness, but have been shown to persist for a year. The test can be negative in the early stages of infection, but the presence of atypical mononuclear cells and a negative IM screen is more likely to be due to other viral infections, most notably CMV or to infection by Toxoplasma gondii.

General presentation can include sore throat, fever, fatigue, weight loss, malaise, pharyngeal inflammation, vomiting, petechiae and loss of appetite. Common signs also include lymphadenopathy, splenomegaly, hepatitis and haemolysis.

Older adults are less likely to have a sore throat or lymphadenopathy but are more likely to present with hepatomegaly and jaundice. Rarer signs and symptoms include thrombocytopenia, with or without pancytopenia, splenic rupture, splenic haemorrhage, upper airway obstruction, pericarditis and pneumonitis. A rare manifestation of mononucleosis is erythema multiforme.