Toxoplasma – Serology
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.
Testing Indications
Serologic testing for Toxoplasmosis may be indicated as part of the investigation and work-up of: 1) Patients suspected of having acute/recent infection with Toxoplasma; 2) Mothers and their newborns when congenital infection is suspected (e.g. ‘TORCH’ screen); 3) Patients with intracranial lesions suspected of being due to Toxoplasma; and 4) Patients to determine evidence of past infection.
Specimen Requirements
Test Requested | Required Requisition(s) | Specimen Type | Minimum Volume | Collection Kit |
Toxoplasma Immunity1 (IgG) |
Serum, Whole Blood, clotted |
600 μl serum or 2.0 ml blood |
Blood, clotted - vacutainer tubes (SST) |
|
Toxoplasma Diagnosis2 (IgG and IgM) |
Serum, Whole Blood, clotted |
600 μl serum or 2.0 ml blood |
Blood, clotted - vacutainer tubes (SST) |
|
Toxoplasma PCR3,4 |
Amniotic fluid |
10.0 ml |
Sterile container |
|
Toxoplasma PCR3,4 |
Whole blood (plasma will be rejected) |
1.0 ml |
EDTA – lavender top tube |
|
Toxoplasma PCR3,4 |
Bronchial Alveolar Lavage (BAL) |
10.0 ml |
Sterile container |
|
Toxoplasma PCR3,4 |
CSF |
1.0 ml |
Sterile container |
|
Toxoplasma PCR3,4 |
Pleural fluid |
600 μl |
Sterile container |
|
Toxoplasma Avidity2,3 |
Serum, Whole Blood, clotted |
The sample used for Toxoplasma Diagnosis, IgM will be used for Avidity |
Submission and Collection Notes
Toxoplasma IgG testing will be performed on all requests for Toxoplasma serology when immunity is requested or when there is no clinical information indicated on the requisition.
Toxoplasma IgG and IgM testing will only be performed when the following clinical information is provided indicating acute/recent infection: clinical or exposure information including but not limited to clinical symptoms, date of onset, contact with a known case, suspected/rule out/or possible congenital infection, exposure to cats and ingestion of poorly/undercooked meat is included on the requisition.
Avidity testing is performed after Toxoplasma IgG and IgM and referred to the Institut national de santé publique du Québec - 945 Wolfe Avenue, Québec, QC., and will be performed under the following conditions:
- the patient is pregnant; and
- both Toxoplasma IgG and IgM are reactive
3. Contact PHO laboratory prior to submitting samples for PCR (Samples can only be delivered to PHO laboratory Monday to Wednesday).
PHO laboratory refers samples for Toxoplasma PCR to the National Reference Centre for Parasitology (NRCP) - Room E03-5375, 1001 Décarie Blvd., Montreal, QC H4A 3J1
Timing of Specimen Collection
IgM antibodies to Toxoplasma are the first to appear and are usually detectable approximately 1 week after the infection. IgM levels peak after 1–3 months and then slowly decline over the next 9 months until undetectable. However, up to 9–27% of those who have been infected with Toxoplasma have detectable IgM antibodies that may remain for 2 years or more. Toxoplasma IgG appears approximately 2 weeks after infection and peaks at 3 months. IgG antibodies then persist for life.
Limitations
Grossly haemolyzed or lipaemic samples as well as samples containing particulate matter or exhibiting obvious microbial contamination are not recommended for testing.
Storage and Transport
Label the specimen container with the patient’s full name, date of collection and one other unique identifier such as the patient’s date of birth or Health Card Number. Failure to provide this information may result in rejection or testing delay.
Special Instructions
Centrifuge if using SST. Place specimen in biohazard bag and seal.
Specimens should be stored at 2-8°C following collection and shipped to PHOL on ice packs.
Test Frequency and Turnaround Time (TAT)
Toxoplasma serology (IgG, IgM) testing is performed daily Monday to Friday.
Turnaround time is up to 5 days from receipt by PHO laboratory.
Toxoplasma IgG and IgM are tested on the DiaSorin Liaison XL™ analyzer. The Toxoplasma IgG and IgM assays are chemiluminescent immunoassays (CLIA) for the determination of IgG and IgM antibodies to Toxoplasma gondii in human serum.
Algorithm
If avidity testing is requested, it will be performed on pregnant patients after Toxoplasma IgG and IgM have tested reactive.
Interpretation
The absence of both Toxoplasma IgG and IgM antibodies indicates no evidence of recent or past infection. The presence of Toxoplasma IgG antibodies with the absence of IgM antibodies indicates evidence of past infection with Toxoplasma. The detection of Toxoplasma IgM antibodies with absence of IgG antibodies suggests recent infection with Toxoplasma – follow-up testing > 2 weeks later should be performed to confirm the development of IgG antibodies and thus recent/acute infection.
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