Seroconversion

Seroconversion is the development of detectable specific antibodies to microorganisms in the blood serum as a result of infection or immunization. Serology (the testing for antibodies) is used to determine antibody positivity. Prior to seroconversion, the blood tests "seronegative" for the antibody; after seroconversion, the blood tests "seropositive" for the antibody.

The word is often used in reference to blood testing for anti-HIV antibodies.

Seroreversion is the opposite of seroconversion. This is when the tests can no longer detect antibodies in a patient’s serum. [Tantalo et al, JID 2005:191; "Treponema pallidum" strain-specific differences in neuroinvasion and clinical phenotype in a rabbit model"]

Background

The immune system maintains an "immunological memory" against past pathogens to facilitate early detection and to confer protective immunity against a rechallenge. This explains why many childhood diseases never recur in adulthood (and when they do, it generally indicates immunosuppression or failure of a vaccine).

In the initial (primary infection) phase of the infection, immunoglobulin M (IgM) antibodies are produced and as these levels drop (and become undetectable) immunoglobulin G (IgG) levels rise and remain detectable. Upon reinfection, IgM antibodies usually do not rise again but IgG levels will increase. Thus an elevated IgM titre indicates recent primary infection, while the presence of IgG suggests past infection or immunization.

References