Toxoplasma gondii IgG
Measures long-lasting IgG antibodies to the Toxoplasma parasite. A positive result means past exposure, not necessarily a recent infection.
AI-verified against cited sources. Awaiting expert reviewAlso called Toxo IgG, T. gondii IgG, TOXO-GLOINC 8039-0
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The usual range for Toxo IgG depends on age. Add your age above to see where you stand.
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What it is
Toxoplasmosis is an infection caused by the parasite Toxoplasma gondii. People can pick it up from undercooked meat, contaminated soil or water, or cat feces, and many people carry it without ever knowing. This test measures IgG antibodies, the long-lasting kind your immune system makes after exposure, in international units per milliliter (IU/mL). Each lab sets its own cutoffs.
Why it matters
Most healthy people who have been infected have no symptoms or only mild ones. The test matters most in pregnancy, for people with weakened immune systems, and when a clinician is checking a newborn or an eye problem. A positive IgG shows that you were infected at some point, but not when. Clinicians compare it with IgM, and sometimes an IgG avidity test, to estimate timing. If you are pregnant, timing matters, so follow up with your prenatal clinician.
If it’s low
A negative result means no Toxoplasma IgG was found, so you probably have not been infected before. It also means you could still catch the infection. If you are pregnant or have a weakened immune system, your clinician can tell you about ways to lower your exposure.
Common causes
- Never having been infected with Toxoplasma
- An infection so recent that antibodies have not appeared yet
What can help
- Ask your clinician about food safety and cat-litter precautions, especially in pregnancy
- If you may have been exposed recently, ask whether a repeat test makes sense
If it’s high
A positive IgG means your immune system has met the Toxoplasma parasite at some point. IgG stays detectable for years, so a positive result by itself does not tell you when the infection happened or whether it is active. In many healthy people it simply reflects past exposure.
Common causes
- A past infection that caused no symptoms, which is common
- A past infection that has resolved
- A recent infection, if IgM is also positive or the IgG is rising
- Antibodies passed from a mother to her newborn in the first months of life (usually under 6 months)
What can help
- Ask your clinician whether an IgM or IgG avidity test is needed, especially in pregnancy
- Ask whether the result should be confirmed at a reference laboratory if the timing of infection matters
What can affect your result
- Time since infection
- Pregnancy and newborn age, since mothers pass IgG to their babies
- A weakened immune system
- The lab's kit and cutoffs
- Each lab's kit has its own cutoffs, and the size of the number does not show how much antibody there is (ARUP), so compare results only from the same lab and method.
- Grossly hemolyzed or very fatty (lipemic) samples may be rejected (Quest).
IgG can stay detectable for years after an infection (Quest).
When to talk to a clinician
A positive IgG on its own is not urgent. If you are pregnant, tell your prenatal clinician promptly about any positive or equivocal toxoplasma result. Contact a clinician soon for swollen lymph nodes with fever or fatigue, or for new blurred vision, eye pain or floaters. If you have a weakened immune system and develop a severe headache, confusion or seizures, call 911 or your local emergency number.
Questions you could ask
- Why was this test ordered, and how will the result change what we do?
- Does my result point to a past or a recent infection, and how can we tell?
- Do I need an IgM or IgG avidity test, or confirmation at a reference laboratory?
- Does this affect my pregnancy care or any other condition I have?
- What precautions should I take to avoid infection, especially if I am pregnant or have a weakened immune system?
Questions people ask
Does a positive IgG mean I have an active infection?
Not necessarily. IgG stays positive for years, so a positive result shows you were infected at some point (CDC). Clinicians use IgM and sometimes an avidity test to estimate timing.
I am pregnant and my IgG is positive. What happens next?
Talk with your prenatal clinician. IgG alone can't say when the infection happened. If timing matters, the CDC recommends follow-up or confirmatory testing, which can include sending blood to a toxoplasma reference laboratory.
Why is the cutoff on my report different from the ones shown here?
Each lab and kit sets its own cutoffs. Quest and ARUP use 7.2 and 8.8 IU/mL, Mayo uses 1 and 3 IU/mL, and other assays differ. Go by the interpretation your lab printed, and compare results only from the same lab.
Show the science and sources
For clinicians and researchers
Quest's immunoassay (test 3679) reports IgG in IU/mL: below 7.20 negative, 7.20 to 8.79 equivocal and above 8.79 positive. ARUP's chemiluminescent immunoassay (test 0050770, LOINC 8039-0) reports 7.1 IU/mL or less as not detected, 7.2 to 8.7 as indeterminate (repeat in 10 to 14 days may help) and 8.8 or more as detected. ARUP states that the magnitude of the result does not indicate the amount of antibody, that the best evidence of current infection is a significant change on two appropriately timed specimens tested together in the same lab, and that the test should not be used for blood donor screening. The CDC states that a positive IgG indicates infection at some time, that IgM can be detected for up to 18 months, and that confirmatory testing is recommended when the timing of infection is important, as in pregnancy; that testing is available at the Jack S. Remington Laboratory for Specialty Diagnostics at Sutter Health in Palo Alto. Quest notes that rising IgG after birth, without a placental leak, is consistent with neonatal infection. Cutoffs differ by assay even though the unit is the same: Mayo's electrochemiluminescence assay (TXPG, LOINC 8039-0) reports under 1 IU/mL as negative, 1 to under 3 as borderline and 3 or more as positive, while Quest and ARUP use 7.2 and 8.8, so the interpretation printed on your report is the one to use. Mayo notes that IgG in infants under 6 months usually comes from the mother.
LOINC 8039-0 (primary), 5388-4, 22580-5. Specimen: serum.
Sources
- Toxoplasma Antibody (IgG) (test code 3679), Quest Diagnostics
- Toxoplasma gondii Antibody, IgG (test 0050770), ARUP Laboratories
- DPDx: Toxoplasmosis, Centers for Disease Control and Prevention
- Toxoplasma gondii Antibody, IgG, Serum (TXPG), Mayo Clinic Laboratories (via testcatalog.org)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.