VCA IgM antibodies indicate acute infection.
VCA IgM antibodies are usually detectable at the time of presentation and disappear after about 4 weeks.
False positives are common in the presence of other infections and false negatives also occur. VCA IgG antibodies develop soon after VCA IgM antibodies and persist for life. Occasionally, VCA IgG antibodies may be detected prior to VCA IgM antibodies.
EBNA antibodies develop 2-3 months post infection, persist for life and indicate past infection.
Current primary infection is thus confirmed if VCA IgM antibodies are present and EBNA IgG is negative. VCA IgG may also be positive.
Recent primary infection is indicated by the presence of VCA IgG antibodies, with low or absent VCA IgM antibodies and low or absent EBNA IgG. Past infection is indicated by the presence of VCA IgG and EBNA antibodies.
Because of individual variations in the response to EBV infection, confirmation of the diagnosis may require 2 specimens collected several weeks apart to demonstrate a change in the pattern of antibodies present. The white cell count, blood film appearance and liver function test results are also helpful. Alternatively, some laboratories are using VCA IgG avidity analysis to differentiate recent from past infection.