Toxoplasmosis is an infection caused by a parasite. The test detects antibodies produced in response to an old or recent infection by the parasite. During infection, the body first produces measurable IgM antibodies in the blood 1 to 2 weeks after infection. A few months later, IgM becomes undetectable and is replaced by IgG antibodies that will be present for the rest of the person’s life. IgM antibodies may reappear if the infection is reactivated or if the infection is chronic. Detection of toxoplasmosis is particularly important in pregnant women because of the high risk (30% to 40%) of transmitting the infection to the fetus. Fetal toxoplasmosis can lead to miscarriages, fetal death and numerous complications (mental retardation, blindness, deafness, etc.).
Negative IgM and IgG results indicate that the person has no immunity against toxoplasmosis and, if a woman becomes infected in early pregnancy, the parasite could be transmitted to the fetus. Positive IgG results indicate that the person is immunized and is not at risk of transmitting the infection to the fetus. If IgM results are also positive, the infection is recent. Negative IgG results with confirmed positive IgM results indicate a recent infection. Inconclusive results should be confirmed on a new specimen 3 weeks after the first test.