Measurement of heterophil antibody and antibodies to EB viral capsid antigen IgG and IgM in suspected cases of infectious mononucleosis.

The EBV IgG titres in acute and convalescent specimens from 97 cases of infectious mononucleosis were compared with titres from acute and convalescent sera from 96 students with illnesses resembling infectious mononucleosis but without heterophil antibody, EB IgM or EB IgG seroconversion; and also with titres from 91 healthy students known to have had EB IgG antibody for at least six months. These titres were related to the titre of the Research Standard A.66/235 for infectious mononucleosis serum prepared by the National Institute for Biological Standards and Control. Serial sera were tested for heterophil antibody and EBVCA specific IgG and IgM from 61 university students with infectious mononucleosis. The period of persistence of heterophil antibody and EBV IgM after illness was outlined from the results of the tests. Single sera from 406 patients in hospital or general practice sent to the diagnostic laboratory for heterophil antibody tests were also tested for EBV antibodies without prior knowledge of the heterophil antibody result. The close agreement between heterophil antibody and EBV IgM results is shown. False positive EB IgM results were correlated with the presence of rheumatoid factor.