Toxoplasma gondii IgM
Looks for IgM antibodies to the Toxoplasma parasite. They appear early in an infection but can linger for a year or more.
AI-verified against cited sources. Awaiting expert reviewAlso called Toxo IgM, T. gondii IgM, TOXO-MLOINC 40678-5
What it is
Toxoplasmosis is an infection caused by the parasite Toxoplasma gondii. IgM is the first kind of antibody your body makes after a new infection, and this test looks for it. Labs usually report the result as negative, equivocal or positive, based on a number printed in arbitrary units per milliliter (AU/mL). The test is usually ordered with the IgG test, because the two are read together.
Why it matters
IgM can be a sign of a recent infection, which makes the test useful in pregnancy and when a clinician suspects a new infection. But Toxoplasma IgM can stay detectable for a year or more, so a positive result does not necessarily mean the infection is recent or ongoing. That is why a positive result in pregnancy is usually confirmed at a reference laboratory before decisions are made.
If it’s low
A negative result means no IgM was found, so a recent infection is less likely. Very early infection can be missed, and IgM may have faded after an older infection.
Common causes
- No recent Toxoplasma infection
- Testing very early, before IgM has risen
- IgM that has already faded after an older infection
What can help
- If infection is still suspected, ask whether a repeat test in a few weeks is useful
If it’s high
A positive result means IgM antibodies to Toxoplasma were found. This can be a sign of a recent infection. It can also be left over from an older infection, since IgM may persist for more than a year, or be a false positive. A positive result needs confirming, especially in pregnancy.
Common causes
- A recent Toxoplasma infection
- An older infection with long-lasting IgM
- A false-positive result, which is why a positive is usually confirmed
What can help
- Ask your clinician about repeat testing on a sample taken 1 to 3 weeks later
- Ask about confirmation at a Toxoplasma reference laboratory
- If you are pregnant, talk with your prenatal clinician promptly about next steps
What can affect your result
- Time since infection
- Pregnancy
- The lab's kit and cutoffs
- IgM that persists after an old infection
- IgM can stay detectable for more than a year after an infection, so a positive result does not prove a recent infection (Quest, ARUP).
- Each lab's kit has its own cutoffs (both Quest and ARUP print numbers in AU/mL), so compare results only from the same lab and method.
- Grossly hemolyzed or very fatty (lipemic) samples may be rejected (Quest).
IgM is typically detected within a few days of infection, peaks within a few weeks, and usually falls to undetectable levels within a few months (Quest).
When to talk to a clinician
If you are pregnant, tell your prenatal clinician promptly about any positive or equivocal toxoplasma IgM result. For anyone else, a positive result needs a conversation with a clinician but is not usually urgent. 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
- How will my IgM result be read together with my IgG result?
- Could this IgM be left over from an older infection?
- Do I need repeat testing or confirmation at a reference laboratory?
- Does this result affect my pregnancy care or any other condition I have?
- If I may have been exposed recently, should I be tested again?
Questions people ask
Does a positive IgM mean I have a new infection?
Not necessarily. Toxoplasma IgM can stay positive for more than a year after an infection, so a positive result alone does not prove a recent or ongoing infection (Quest, CDC). Your clinician will read it with your IgG result and your situation.
Why might my lab want to retest in a few weeks?
ARUP, citing the CDC, advises retesting any indeterminate or positive IgM on a sample collected 1 to 3 weeks later, run alongside the first. A change between the two samples helps show whether the infection is new.
I am pregnant and my IgM is positive. What happens next?
Talk with your prenatal clinician promptly. A positive IgM in pregnancy is usually sent for confirmation at a reference laboratory that does a panel of toxoplasma tests, because the timing of infection matters for the pregnancy.
Show the science and sources
For clinicians and researchers
Quest's immunoassay (test 37207) reports IgM in AU/mL: below 8.00 negative, 8.00 to 9.99 equivocal and above 9.99 positive. ARUP's semi-quantitative chemiluminescent immunoassay (test 0050557, LOINC 8040-8, DiaSorin LIAISON) reports 7.9 AU/mL or less as not detected, 8.0 to 9.9 as indeterminate and 10.0 or more as detected. Quest states that IgM is typically detected within days of infection, peaks within weeks and usually falls to undetectable levels within months, though in some patients it persists for more than a year. The CDC notes that IgM may be detected for as long as 18 months. ARUP, citing the CDC, advises retesting any indeterminate or detected IgM in parallel with a specimen collected 1 to 3 weeks later, with further confirmation at a reference laboratory using a different test (an IgM ELISA); it adds that caution should be used with IgM in prenatal screening and that, in pregnancy, a detected IgM confirmed by a second reference laboratory calls for further evaluation by the pregnancy care team. In nonpregnant patients with an indeterminate or detected result, PCR on a specimen from an affected body site may help. The CDC says confirmatory testing is recommended when the timing of infection is important, as in pregnancy, and that it is available at the Jack S. Remington Laboratory for Specialty Diagnostics at Sutter Health in Palo Alto.
LOINC 40678-5 (primary), 8040-8, 25542-2, 5390-0. Specimen: serum.
Sources
- Toxoplasma Antibody (IgM) (test code 37207), Quest Diagnostics
- Toxoplasma gondii Antibody, IgM (test 0050557), ARUP Laboratories
- DPDx: Toxoplasmosis, Centers for Disease Control and Prevention
- Toxoplasma gondii Antibody, IgM, Serum (TXPM), 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.