Diagnosis of toxoplasmosis in pregnancy: importance of immunoglobulin G avidity test.

The immunoglobulin G (IgG) avidity test has proved to be a highly useful test in the diagnosis of toxoplasmosis during pregnancy, especially in combination with conventional serological assays. Acute infections at the time of gestation predispose the offspring to the risk of congenital toxoplasmosis. The IgG avidity test was developed to differentiate between recent and more distant infection; this method is valuable in the situation in which a single serum sample is obtained in the first trimester of pregnancy. This paper describes the utility of IgG avidity test during pregnancy, and its role in ruling out, by a high avidity, a recently acquired infection. Testing for specific IgG avidity has been reported to be useful for confirmatory testing in patients who have positive IgG and IgM antibodies.