Toxoplasma – Serology

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 Collection and Handling

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 Avidity2,3

Serum, Whole Blood, clotted

The sample used for Toxoplasma Diagnosis, IgM will be used for Avidity

Submission and Collection Notes

1

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.

2

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.

3

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

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.

Preparation Prior to 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.

Requisitions and Kit Ordering

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.

Reporting

Results are reported to the ordering physician or health care provider as indicated on the requisition.

Test Methods

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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Laboratory Services

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Updated 22 Oct 2019