Relevance of Avidity Testing of VCA IgG in EBV Diagnostics

Diagnostics of Epstein-Barr virus (EBV) primary infection is usually based on the results of ELISA determination of IgM and IgG against viral capsid antigen (anti-VCA IgM and anti-VCA IgG) and of IgG against EBV nuclear antigen (anti-EBNA-1 IgG). In cases of difficult interpretation, the use of additional tests, such as measurement of IgG avidity, may help to determine the infection stage. IgG maturation occurs several weeks after primary infection, and the presence of high-grade antibodies is a marker for a previous infection. In this study, we determined the significance of the avidity of anti-VCA IgG avidity test for patients with infectious mononucleosis or suspected EBV reactivation. Serological ELISA was used to determine the avidity of IgG against viral capsid antigen (anti-VCA IgG) in 46 single serum samples. Low anti-VCA IgG avidity was found in 26% (95% CI: 14% - 41%) of all tested samples, which could be interpreted as acute infection. Our results confirmed the presence of isolated IgG models in 24% (95% CI: 11%-42%) of primary EBV infections, while possible reactivation or non-specific reactivity of anti-VCA IgM was suggested for 69% (95% CI: 39%-91%) of the positive anti-VCA IgM/IgG patients. Our results show that the laboratory confirmation of patients with clinical evidence of infectious mononucleosis and absence of IgM should include the use of avidity tests. We believe that avidity tests may be useful for the discrimination between reactivation and primary infections.