VHOSPITAL.CLINIC · Serology Test
Toxoplasma IgG/IgM serology (ELISA) is the cornerstone of toxoplasmosis diagnosis — determining immune status, timing of infection, and risk to immunocompromised patients and pregnant women.
Enzyme-linked immunosorbent assay detecting IgG/IgM antibodies against parasite-specific antigens — used for diagnosis, monitoring, and surveillance.
IgM appears within 1–2 weeks of primary infection and typically falls below detectable levels within 3–6 months. IgG rises after 2–4 weeks, peaks at 1–2 months, then remains elevated for life. The IgG/IgM combination and avidity testing determine timing of infection — critical for pregnancy risk stratification.
Venous blood sample (5 mL). Laboratory ELISA measures IgG (in IU/mL) and IgM (index value). Reference ranges vary by laboratory. Serial samples (2–4 weeks apart) showing IgG seroconversion or 4-fold rise confirm acute infection. A single positive IgG only indicates past exposure.
IgG−/IgM−: seronegative — not exposed, susceptible. IgG+/IgM−: past infection, immune — low risk. IgG+/IgM+: recent or acute infection (confirm with avidity test). IgG−/IgM+: very early infection or false positive. IgG rising on serial samples: acute infection. In pregnancy: any IgM+ requires avidity testing.
IgG ELISA sensitivity: >98%. IgM ELISA sensitivity: 75–95% (false positives common). IgG specificity: >99%. IgM specificity: 85–95% (commercial IgM assays have 10–15% false positive rate — IgM alone should not diagnose acute infection).
A positive IgM suggests recent primary toxoplasma infection within the past 3–6 months — but IgM can also remain elevated for up to 18 months in some patients, and commercial tests have a 10–15% false positive rate. Always combine with avidity testing to determine timing of infection accurately.
Yes, in immunocompetent individuals. Positive IgG with negative IgM indicates past infection and immunity — toxoplasmosis is not a current risk. In immunocompromised patients (HIV, transplant), past infection carries reactivation risk when immunity falls (CD4 <100 in HIV).
Primary toxoplasma infection during pregnancy can cause congenital toxoplasmosis — miscarriage, stillbirth, or severe neonatal disease (hydrocephalus, chorioretinitis, developmental delay). First-trimester serology establishes baseline immune status. Seroconversion during pregnancy requires immediate spiramycin treatment and specialist referral.
Toxoplasmosis is caused by the parasite Toxoplasma gondii, transmitted through cat feces, undercooked meat, or vertically to the fetus. It is usually asymptomatic in healthy individuals but can cause severe disease in immunocompromised patients and congenital infection.
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