Toxoplasma gondii Antibodies, IgG

The Toxoplasma gondii Antibodies, IgG assay (also known as Antitoxo-IgG or toxoplasmosis IgG) is used to document immune status to T. gondii in preconception and prenatal care and to support evaluation of suspected toxoplasmosis in immunocompromised patients. Quantitative IgG provides evidence of previous exposure. When the timing of infection is clinically relevant, such as during pregnancy, concurrent IgM testing is recommended and, if IgG and IgM are both reactive, IgG avidity testing is added to help distinguish recent from remote infection.

Toxoplasma gondii is widespread, and members of the cat family serve as the definitive host. Oocysts shed in cat feces become infectious within days and can persist in the environment. Humans typically acquire infection by ingesting tissue cysts in undercooked meat or oocysts from contaminated soil, water, or produce; transplacental transmission also occurs, while infection via transplantation or transfusion is rare. In immunocompetent individuals, infection is often inapparent or produces a mild, self-limited febrile illness. In immunocompromised patients, reactivation or primary infection may result in ocular or central nervous system disease, including chorioretinitis and encephalitis. Primary infection during pregnancy carries a 30%–40% risk of fetal transmission, with earlier gestation associated with more severe outcomes such as miscarriage, stillbirth, or severe neonatal disease. After exposure, IgM appears early, and IgG develops within weeks, increases during the acute phase, and then stabilizes at a lower level long term; measurable IgG typically persists for life. Quantitative IgG, interpreted alongside IgM and, when indicated, IgG avidity testing, helps differentiate remote from recent infection in appropriate clinical contexts.