Toxoplasma (Toxoplasmosis) – Antibody, Avidity, PCR, and Microscopy

Consistent with O. Reg. 671/92 of the French Language Services Act, laboratory testing information on this page is only available in English because it is scientific or technical in nature and is for use only by qualified health care providers and not by members of the public.

Background
This page provides antibody (serology), avidity, PCR, and microscopy testing information for toxoplasmosis at Public Health Ontario (PHO). The causative agent of toxoplasmosis is the parasitic apicomplexan protozoon Toxoplasma gondii (felid definitive host). Infections occur worldwide following ingestion of infectious oocysts from the environment contaminated by felid feces (e.g. contaminated food or water), ingestion of undercooked meat or shellfish containing dormant bradyzoites, vertical transmission during pregnancy, organ transplantation, or rarely blood transfusion. Toxoplasmosis manifestations include non-specific acute febrile illness (e.g. flu-like illness and/or lymphadenopathy), ocular infection (e.g. posterior uveitis), encephalitis (e.g. cortical or basal target-like ring-enhancing brain lesions), pneumonitis (e.g. reticulonodular infiltrates), carditis (e.g. arrhythmias or heart failure), or congenital infection (e.g. as per other manifestations along with intracranial calcifications, hydrocephalus, hepatosplenomegaly, jaundice, or thrombocytopenic purpura).

Updates

Updated to consolidate the Toxoplasma microscopy, PCR and serology testing information into a single Testing information webpage.

*Uncontrolled print copy. Valid only on day of print: 28 Oct 2026.

Testing Indications

IgG antibody testing may be considered for:

Targeted screening of asymptomatic individuals at high risk of developing reactivated toxoplasmosis due to an impaired immune system (e.g., HIV with CD4 less than 200 cells/mm3, biologic therapies, chemotherapies, immunotherapies, heart transplantation, bone marrow transplantation).

IgG and IgM antibody testing may be considered for:

Targeted screening of asymptomatic pregnant* individuals at high risk of developing acute toxoplasmosis and subsequent congenital transmission due to their exposure history.
Diagnosis of symptomatic individuals with compatible clinical presentation for toxoplasmosis (e.g. acute febrile illness, ocular infection, encephalitis, pneumonitis, carditis, or congenital infection).

*Note: If a pregnant individual is already known to have a positive IgG serostatus from testing conducted prior to their current pregnancy, the individual is usually considered a low risk of congenital transmission and screening is not recommended in this scenario.

Avidity testing is mainly reserved for infected pregnant individuals with positive IgG and IgM serology during their first trimester to determine if an infection was most likely acquired at least 16 weeks prior (i.e. before conception).

PCR testing (± microscopy) may additionally be considered for the diagnosis of active infection in individuals with compatible clinical presentation for toxoplasmosis if serology is positive or if there is suspicion of a falsely negative serology result (e.g. impaired immune system).

Note: Toxoplasma IgA and IgE testing is not available at PHO.

Acceptance/Rejection Criteria

IgG antibody testing will be performed on all serology requests.

IgM antibody testing will only be performed if any of the following criteria is documented on the requisition form:

Clinical signs or symptoms consistent with toxoplasmosis,
Pregnancy or perinatal status AND relevant exposure (e.g. felid feces, undercooked meat)

Avidity testing will only be performed if both of the following criteria are documented on the requisition form:

Toxoplasma IgM positive and IgG positive status
Pregnancy or perinatal status

Specimen Collection and Handling

Specimen Requirements

Test Requested	Required Requisition(s)	Specimen Type	Minimum Volume	Collection Kit
Toxoplasma – IgG	General Test Requisition	Serum	1.0 ml	Red top (clotted) tube or serum separator tube (SST)
Toxoplasma – IgG and IgM	General Test Requisition	Serum	1.0 ml	Red top (clotted) tube or serum separator tube (SST)
Toxoplasma – Avidity	General Test Requisition	Serum	1.0 ml	Red top (clotted) tube or serum separator tube (SST)
Toxoplasma – PCR	General Test Requisition	EDTA blood, Body fluid or tissue specimen (e.g., amniotic fluid, broncho-alveolar lavage, CSF, pleural fluid, ocular fluid, urine, any tissue biopsy - fresh or in Paraffin block)	0.5 ml minimum but at least 1.0 ml recommended (fluid) or 0.2 g (tissue)	Sterile container
Toxoplasma – Microscopy	General Test Requisition	Body fluid or tissue specimen (e.g., amniotic fluid, broncho-alveolar lavage, CSF, pleural fluid, ocular fluid, urine, tissue biopsy)	0.5 ml minimum but at least 1.0 ml recommended (fluid) or 0.2 g (tissue)	Sterile container

Submission and Collection Notes

Complete all fields of the requisition form.

Confirm that the correct information is listed on the requisition as per the Acceptance/Rejection Criteria section above.

For serology, PHO prefers centrifuged SST for serological testing. Generally, only one full 5 mL SST is sufficient for testing a combination of up to six infectious disease serology markers. If a full tube cannot be drawn and more than six markers are requested, submit two tubes. Refer to Serology Testing – Laboratory Specimen Collection and Submission Instructions for more information.

Label the specimen container(s) with the patient’s first and last name, date of collection, and one other unique identifier such as the patient’s date of birth or Health Card Number. For additional information see: Criteria for Acceptance of Patient Specimens. Failure to provide this information may result in test cancellation or testing delay.

CSF antibodies may be detectable in patients with encephalitis, and ocular fluid antibodies may be detectable in patients with ocular infection, but these are not validated specimen types for antibody testing and require approval. If needed, contact PHO’s customer service for information.

Timing of Specimen Collection

For serology: If a recent infection is suspected following exposure, a repeat collection of a convalescent serum sample (2-3 weeks later) may be beneficial since serology testing can be negative during the first week of the acute phase of illness.

Limitations

For serology: Grossly haemolysed, lipemic, contaminated specimens, and specimens containing anti-coagulant are unsuitable for testing.

Storage and Transport

For serology: Centrifuge tube if using serum separator tube (SST).

Place specimen container in a biohazard bag and properly seal the bag. Specimens should be stored at 2-8°C and shipped to PHO on ice packs within 48 hours of collection. If delays beyond 48 hours of collection are expected, samples can be stored at -20°C and shipped to PHO on dry ice.

All clinical specimens must be shipped in accordance with the Transportation of Dangerous Good Act.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Toxoplasma IgG and IgM antibody testing is performed daily from Monday to Saturday at PHO’s laboratory in Toronto. Turnaround for IgG and IgM antibody testing is up to 5 calendar days from receipt at PHO’s laboratory.

Toxoplasma avidity testing is referred to the Laboratoire de santé publique du Québec (LSPQ) in Montreal. Turnaround time for avidity testing is up to 40 days from receipt at PHO’s laboratory.

Toxoplasma PCR is referred to the National Reference Centre for Parasitology (NRCP) in Montreal. Turnaround time for PCR testing is up to 40 calendar days from receipt at PHO’s laboratory.

Toxoplasma microscopy is performed daily from Monday to Friday at PHO’s Toronto site. Turnaround time for microscopy is up to 3 calendar days from receipt at PHO’s laboratory.

Test Methods

Toxoplasma IgG and IgM antibody testing is performed at PHO using the DiaSorin LIAISON chemiluminescence immunoassay (CLIA) based on inactivated T. gondii (RH strain) antigens obtained from sonicated and detergent-extracted trophozoites.

Toxoplasma avidity testing is performed at the LSPQ using the bioMérieux VIDAS TOXO IgG Avidity enzyme linked fluorescent assay (ELFA) based on the relative fluorescence value (RFV) of IgG antibodies before and after urea dissociation of antibody-antigen linkages. If the RFV still remains high after dissociation (e.g. ≥ 30% of the initial RFV), the IgG demonstrates high binding avidity suggestive of past infection (acquired at least 16 weeks prior).

Toxoplasma PCR is performed at the NRCP using a specific T. gondii B1 gene target based on Bretagne S et al. (1993).

Toxoplasma microscopy is performed at PHO using direct wet mount and Giemsa staining.

Performance and Limitations:
Toxoplasma IgG antibody sensitivity using the LIAISON assay has a reported sensitivity of 94.8% and specificity of 99.5%. With other assays, Toxoplasma IgG sensitivity has been reported to vary from 86.6-94.0% and specificity from 92.4-97%. Toxoplasma IgM antibody sensitivity using the LIAISON assay has a reported sensitivity of 96.7% and specificity of 96.8%. With other assays, Toxoplasma IgM sensitivity has been reported to vary from 63.4-83.1% and specificity from 88.8-97.9%. When combined, the sensitivity of both IgG and IgM has been reported to vary from 89.4-97.5% and the specificity from 93.9-98.3%.

Overall, IgG and IgM antibody sensitivity may be lower in localized ocular infections or individuals with impaired immunity. A negative antibody result may also be seen in very early infection, as IgM antibodies may take 1-2 weeks and IgG antibodies may take 2-3 weeks to become detectable following infection. Seropositivity may be affected by treatment or prophylaxis. Both IgM and IgG antibodies may persist for years following infection and neither may be able to distinguish between recent, past, or reactivated infection. Background seropositivity in Ontario has been previously reported to vary from under 5% to over 20% depending on risk factors (higher in Inuit and immigrated communities). Transient IgM antibodies may also infrequently appear years later in individuals with chronic infection. Due to the potential for nonspecific IgM reactions, an isolated IgM result cannot be used on its own to diagnose infection in the absence of documented IgG seroconversion. Recent intravenous immunoglobulins (IVIG) administration has also been reported to cause potential false positive antibody test results.

In infants, maternally transferred IgG antibodies may persist for 6-12 months after birth, therefore a positive IgG in infants does not necessarily confirm congenital infection unless the IgG antibodies persist past 12 months. Similarly, maternally transferred IgM antibodies may be observed up to 5 days after birth, therefore IgM antibody testing at least 5 days after birth may be needed to confirm congenital infection. Sensitivity of IgM testing has been reported to range from 44-81% and serial serum samples may be needed to improve sensitivity during the first 3 months after birth. Infant IgM antibodies may be negative if maternal infection occurred early in the first trimester or if maternal treatment was received. Although not available at PHO, some centres also include IgA antibody testing to diagnose infants with reported benefits in sensitivity ranging from an additional 0-15% over standalone IgM antibody testing.

Toxoplasma avidity testing using the VIDAS assay has a reported positive predictive value of 100% for high avidity results predicting past infection (acquired at least 16 weeks prior). However, low avidity results is not a reliable predictor acute infection, since most infected patients can still harbour low avidity antibodies six months post-infection, and up to 25% of patients with years-long infection may similarly show low avidity antibodies, especially those with an impaired immune system.

Toxoplasma PCR testing performance is reported to have 99% sensitivity and 100% specificity by the NRCP. With other assays, sensitivity has been reported to vary from 51.9-92.2% and specificity from 94.3-97.5%. Sensitivity varies widely with the specimen type, volume used, disease severity, prior treatment, and immune system impairment, including for amniotic fluid (81-98%), ocular fluid (25-85%), CSF (11-77%), and whole blood (15-85%). In pregnancy, PCR sensitivity on amniotic fluid increases with gestational age and is usually not recommended prior to 18 weeks of gestation.

Toxoplasma microscopy directly on body fluid and tissue specimens has very poor sensitivity overall (< 1%) but has rarely been reported positive in severely acute or disseminated infections for patients with an impaired immune system. Such microscopy detections have primarily been described on respiratory and CSF samples. Otherwise, histopathological identification may occasionally support the diagnosis in challenging cases if available locally.

Algorithm

If the patient is pregnant and the results show reactive IgG and IgM antibodies, avidity testing will automatically be reflexed on the sample.

Microscopy will only be performed on body fluid and tissue specimens if specifically requested on the test requisition.

Interpretation

For Toxoplasma IgG and/or IgM antibody testing results (“Toxoplasmosis IgG CLIA” and “Toxoplasmosis IgM CLIA”):

Toxoplasmosis IgG CLIA	Toxoplasmosis IgM CLIA	Interpretation
Reactive	Not performed*	Toxoplasmosis IgG antibodies detected. Suggestive of Toxoplasma infection. Does not distinguish between acute, past, or reactivated infection. May represent maternally transferred antibodies if tested within 12 months after birth.
Indeterminate	Not performed*	Toxoplasma IgG antibody status inconclusive. Clinical correlation required and repeat collection in 2-3 weeks may be considered if clinically indicated; the same results obtained after recollection would imply a low likelihood of Toxoplasma infection.
Non-reactive	Not performed*	Toxoplasmosis IgG antibodies NOT detected. Does not rule out infection, especially if tested in acute infection, with impaired immune system, or following treatment. If an acute infection is suspected, repeat collection in 2-3 weeks with both IgG and IgM is recommended to document seroconversion.
Reactive	Reactive	Toxoplasma IgG and IgM antibodies detected. Suggestive of Toxoplasma infection. Does not distinguish between acute, past, or reactivated infection. If the patient is in their first trimester of pregnancy, avidity testing may be requested to rule in a past infection (acquired at least 16 weeks prior).
Reactive	Indeterminate	Toxoplasma IgG antibodies detected but Toxoplasma IgM antibody status inconclusive. Suggestive of Toxoplasma infection. Does not distinguish between acute, past, or reactivated infection. If the patient is in their first trimester of pregnancy, avidity testing may be requested to rule in a past infection (acquired at least 16 weeks prior).
Reactive	Non-reactive	Toxoplasma IgG antibodies positive and Toxoplasma IgM antibodies negative. Suggestive of past Toxoplasma infection (acquired at least 16 weeks prior). Does not rule out reactivated infection. If the patient is in their first trimester of pregnancy, the patient is considered at low risk for congenital transmission and further Toxoplasma antibody screening is no longer recommended.
Indeterminate	Reactive	Toxoplasma IgM antibodies detected but Toxoplasma IgG antibody status inconclusive. May suggest acute Toxoplasma infection or nonspecific (false) seroreactivity. If clinically indicated, repeat collection in 2-3 weeks with both IgG and IgM is recommended to document seroconversion; the same results obtained after recollection would imply a low likelihood of Toxoplasma infection.
Non-reactive	Reactive	Toxoplasma IgM antibodies detected and Toxoplasma IgG antibodies not detected. May suggest acute Toxoplasma infection or nonspecific (false) seroreactivity. If clinically indicated, repeat collection in 2-3 weeks with both IgG and IgM is recommended to document seroconversion; the same results obtained after recollection would imply a low likelihood of Toxoplasma infection.
Non-reactive	Indeterminate	Toxoplasma IgG antibodies not detected and Toxoplasma IgM antibody status inconclusive. Clinical correlation required and repeat collection in 2-3 weeks may be considered if clinically indicated; the same results obtained after recollection would imply a low likelihood of Toxoplasma infection.
Indeterminate	Non-reactive	Toxoplasma IgM antibodies not detected and Toxoplasma IgG antibody status inconclusive. Clinical correlation required and repeat collection in 2-3 weeks may be considered if clinically indicated; the same results obtained after recollection would imply a low likelihood of Toxoplasma infection.
Non-reactive	Non-reactive	Toxoplasma IgG and IgM antibodies not detected. Does not rule out infection, especially if tested in acute infection, with impaired immune system, or following treatment. If an acute infection is suspected, repeat collection in 2-3 weeks with both IgG and IgM is recommended to document seroconversion. If the patient is in their first trimester of pregnancy, the patient is still considered at risk of acquiring acute toxoplasmosis in the future and appropriate preventive counselling is recommended.

*IgM testing should be requested to facilitate interpretation if testing is for the clinical diagnosis of symptomatic individuals with suspected toxoplasmosis or for asymptomatic screening in pregnancy.

For Toxoplasma avidity testing results (“Toxo IgG Avidity”):

Toxoplasma gondii avidité IgG/ EIA	Résultat	Interpretation
≥ 0.300	Avidité forte	High avidity Toxoplasma antibodies detected. Suggestive of past Toxoplasma infection (acquired at least 16 weeks prior). Does not rule out reactivated infection. If the patient is in their first trimester of pregnancy, the patient is considered at low risk for congenital transmission and further Toxoplasma antibody screening is no longer recommended.
0.200 to 0.299	Equivoque	Toxoplasma antibody avidity status inconclusive. Clinical/exposure correlation required and repeat testing may be considered if clinically indicated.
< 0.200	Avidité faible	Low avidity Toxoplasma antibodies detected. Does not distinguish between acute, past, or reactivated infection. If the patient is in their first trimester of pregnancy, appropriate counselling and further investigations (e.g. amniotic fluid PCR) may be considered if clinically indicated.

For Toxoplasma PCR testing results:

Toxoplasma PCR	Interpretation
Detected	Toxoplasma DNA present.
Indeterminate	Inconclusive result. An indeterminate PCR result may be due to a low level of target genetic material in the specimen, inadequate specimen content, or a non-specific signal. Please resubmit another specimen for testing if clinically indicated.
Not Detected	Toxoplasma DNA not present. Does not rule out infection. Clinical/exposure correlation required.
Invalid	No result available. Test results are invalid due to the failed amplification of the extraction control. Amplification failure may be due to inadequate specimen content, extraction failure, or PCR inhibition. Please resubmit another specimen for testing if clinically indicated.

For Toxoplasma microscopy testing results:

Parasite Microscopy	Interpretation
Parasite(s) found: Toxoplasma gondii	Suggestive of acute or reactivated infection. Clinical/exposure correlation required.
Parasite(s) NOT found	Does not rule out infection. Refer to PCR for additional results.

Reporting

Results are reported to the physician, authorized health care provider (General O. Reg 45/22, s.18) or submitter as indicated on the requisition.

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