2150. Epstein-Barr virus (capsid antigen), avidity of IgG antibodies

An IgG antibody avidity test to the Epstein-Barr virus (EBV) capsid antigen helps determine the duration of infection – whether it occurred recently or long ago. This is especially important when acute mononucleosis is suspected or for risk assessment in pregnant women.

Epstein-Barr virus (EBV, herpesvirus type 4) is one of the most common human viruses, transmitted through bodily fluids, primarily saliva. According to the WHO, up to 95% of adults have antibodies to EBV, indicating a history of infection. Primary infection usually occurs in childhood or adolescence and can manifest as infectious mononucleosis—an illness characterized by fever, sore throat, lymphadenopathy, and hepatosplenomegaly. In many cases, the primary infection is asymptomatic or minimally symptomatic, especially in children.

After infection, EBV persists in the body in a latent state in B lymphocytes throughout life. In adults, especially those with immunosuppression, the following are possible:

• reactivation of the infection;
• development of chronic EBV syndrome;
• or association with lymphoproliferative and oncohematological diseases (Burkitt's lymphoma, Hodgkin's disease, nasopharyngeal carcinoma, post-transplant lymphomas, etc.). After the primary infection, the body produces specific IgM antibodies and soon IgG antibodies to the viral capsid antigen (VCA-IgG).

In the early stages, these IgG antibodies have low avidity, meaning they bind weakly to the antigen. Over time, as the immune response matures, a high-avidity pool of antibodies forms, which binds strongly to viral antigens.

Clinical significance:

• Low IgG avidity → indicates a recent infection (within the last 2-4 months). This is important for confirming the acute or recent phase of the disease, especially when IgM levels may be questionable or have already disappeared.
• High IgG avidity → indicates a past infection and the development of persistent immunity.

• If acute infectious mononucleosis is suspected.
• For pregnant women – to assess the risk to the fetus with positive IgM or IgG results.
• If serological results are inconclusive (IgM+ / IgG+).
• To differentiate between acute and chronic infection.
• For enlarged lymph nodes, general weakness, sore throat, or enlarged spleen or liver.
• To assess immune status with respect to EBV before immunosuppressive therapy.

• Venous blood

In order to exclude factors that may affect the test results, we recommend to follow the preparation rules: