TOXOPLASMA VIRCLIA®

Toxoplasma gondii serology

• Positive IgG indicates previous exposure to Toxoplasma gondii, but does not by itself determine when the infection occurred.

• Qualitative IgG helps identify seronegative and susceptible patients, especially in pregnancy screening.

• Quantitative IgG may support serological follow-up. Seroconversion or a significant increase in IgG in paired samples collected 2–4 weeks apart and analysed with the same method suggests recent infection.

• A positive IgM result may suggest recent infection, but it should be interpreted with caution, as it may persist for months or years and may show non-specific reactivity.

• In IgG-positive / IgM-positive profiles, IgG avidity helps differentiate recent infection from past infection, especially during pregnancy.

• High avidity supports past infection and helps exclude a recently acquired infection.

• Low or intermediate avidity does not confirm recent infection on its own; it should be assessed together with IgG, IgM, serological follow-up and the clinical context.

• In pregnant women with suspected recent infection, maternal serology may require confirmation or complementary techniques, such as PCR in amniotic fluid when indicated.

• In neonates, IgG should be interpreted with caution because of maternal transfer. Persistence of IgG during follow-up or detection of specific IgM supports congenital infection.

• In immunocompromised patients, serology has limitations for the diagnosis of active disease; direct detection techniques may be required depending on the clinical presentation.

Sources: 

• Centers for Disease Control and Prevention. Toxoplasmosis: clinical overview. Atlanta: CDC; [consulted 2026 Jul 1]. Available from: Clinical Overview of Toxoplasmosis

• Centers for Disease Control and Prevention. DPDx: toxoplasmosis. Atlanta: CDC; [consulted 2026 Jul 1]. Available from: https://www.cdc.gov/dpdx/toxoplasmosis/index.html