What this test measures
Toxoplasma IgM is the first antibody the immune system makes after Toxoplasma gondii infection. It typically appears within 1–2 weeks of exposure, peaks at 4–6 weeks, and declines over 3–9 months — though in some individuals it can persist for over a year, which complicates interpretation.
A positive Toxoplasma IgM by itself does not always confirm recent infection. Confirmation in pregnancy requires an IgG avidity test (low avidity suggests recent infection, high avidity suggests infection more than 4 months earlier) and often a repeat sample 2–3 weeks later.
Why it matters
In pregnancy, distinguishing a recent toxoplasma infection from a remote one is critical because primary infection during pregnancy can cause congenital toxoplasmosis (hydrocephalus, chorioretinitis, intracerebral calcification, developmental delay) — while a remote infection poses no fetal risk. Early treatment of acute maternal infection with spiramycin reduces transmission to the fetus, so prompt and accurate diagnosis matters.
In immunosuppressed patients (HIV with low CD4, post-transplant, on chemotherapy), reactivation of latent toxoplasma can cause severe encephalitis or chorioretinitis; testing strategies and treatment differ, and a specialist should manage these cases.
How to prepare
No fasting required. Mention pregnancy status, immunosuppression, recent flu-like illness, or known exposure (raw meat, cat litter) to your doctor and the lab.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Toxoplasma IgM (AU/mL or Index)[1][2] | Negative | — | Positive — possible recent infection, but the IgM can persist for over a year and false positives occur. In pregnancy, an IgG avidity test, paired sampling, and sometimes amniotic fluid PCR are needed for confirmation. Specialist input (infectious disease + obstetrics) is essential. |
Toxo IgM + IgG combined interpretation
| IgG | IgM | Interpretation |
|---|---|---|
| Negative | Negative | Susceptible — take exposure precautions |
| Positive | Negative | Past infection, immune — reassuring in pregnancy |
| Negative | Positive | Possible very early acute infection — repeat in 2 weeks |
| Positive | Positive | Possible recent infection — IgG avidity test required |
Frequently asked questions
I am pregnant and IgM positive — is my baby in danger?
Not necessarily. A positive IgM can persist long after the actual infection. Your doctor will order an IgG avidity test and may repeat sampling 2–3 weeks later. If recent infection is confirmed, spiramycin (and sometimes amniocentesis with PCR) is offered.
How long can Toxo IgM stay positive?
In some people, more than a year. This is the main interpretation challenge — a positive IgM does not automatically mean a recent infection.
Can the IgM test be falsely positive?
Yes — non-specific binding, rheumatoid factor, and assay cross-reactivity can produce false positives. Confirmatory testing in a reference laboratory may be required, especially in pregnancy.
What is the IgG avidity test?
A specialised test that measures how tightly IgG antibodies bind to toxoplasma antigens. Low avidity = recent infection (within 4 months). High avidity = infection more than 4 months ago. It is the single most useful test to time a toxoplasma infection in pregnancy.
What about toxoplasmosis in HIV patients?
In HIV patients with low CD4, latent toxoplasma can reactivate as toxoplasma encephalitis. Diagnosis usually relies on imaging, CSF PCR, and IgG status, not IgM. This is a specialist scenario.
Are there preventive measures I can take?
Yes — well-cooked meat, washed vegetables, wearing gloves when gardening, avoiding handling cat litter, and washing hands well after touching raw meat or soil. Pregnant women and immunosuppressed patients should be especially careful.
How fast does the report come?
NABL-accredited Mumbai and Thane labs typically deliver Toxo IgM reports within 24 hours.
Related Infectious Disease tests
Tests commonly ordered alongside TOXO GONDII - IgM, or that help interpret an unexpected result.
Sources & references
- CDC — Toxoplasmosis · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — Toxoplasmosis Tests · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Toxoplasmosis · accessed 2026-05-30T00:00:00.000Z
- FOGSI India — Antenatal Screening · accessed 2026-05-30T00:00:00.000Z
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