Test Id : TXPAB

For more information see Meningitis/Encephalitis Panel Algorithm.

Supplies: Sarstedt Aliquot Tube, 5 mL (T914)

Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 0.7 mL

Collection Instructions: Centrifuge and aliquot serum into plastic vial.

0.7 mL

Qualitative detection of IgM and quantitative detection of IgG antibodies to Toxoplasma gondii in human serum

For more information see Meningitis/Encephalitis Panel Algorithm.

Toxoplasma gondii is an obligate intracellular protozoan parasite capable of infecting a variety of intermediate hosts, including humans. Infected definitive hosts (cats) shed oocysts in feces that rapidly mature in the soil and become infectious. Toxoplasmosis is acquired by humans through ingestion of food or water contaminated with cat feces or through eating undercooked meat containing viable oocysts. Vertical transmission of the parasite through the placenta can also occur, leading to congenital toxoplasmosis. Following primary infection, T gondii can remain latent for the life of the host; the risk for reactivation is highest among individuals who are immunosuppressed.

Seroprevalence studies performed in the United States indicate approximately 6.7% of individuals aged 12 to 49 years have antibodies to T gondii.

Infection of immunocompetent adults is typically asymptomatic. In symptomatic cases, patients most frequently present with lymphadenopathy and other nonspecific constitutional symptoms, making definitive diagnosis difficult to determine.

Severe-to-fatal infections can occur among patients with AIDS or individuals that are otherwise immunosuppressed. These infections are thought to be caused by reactivation of latent infections and commonly involve the central nervous system.

Transplacental transmission of the parasites resulting in congenital toxoplasmosis can occur during the acute phase of acquired maternal infection. The risk of fetal infection is a function of the time at which acute maternal infection occurs during gestation. The incidence of congenital toxoplasmosis increases as pregnancy progresses; conversely, the severity of congenital toxoplasmosis is greatest when maternal infection is acquired early during pregnancy. Many infants infected in utero are asymptomatic at birth, particularly if maternal infection occurs during the third trimester, with sequelae appearing later in life. Congenital toxoplasmosis results in severe generalized or neurologic disease in about 20% to 30% of the infants infected in utero; approximately 10% exhibit ocular involvement only, and the remainder are asymptomatic at birth. Subclinical infection may result in premature delivery and subsequent neurologic, intellectual, and audiologic defects.

Toxoplasma IgM

Negative

Toxoplasma IgG

Negative

<1 IU/mL Negative

> or =1-<3 IU/mL Borderline

> or =3 IU/mL Positive

Reference values apply to all ages.

Negative: No IgM or IgG antibodies to Toxoplasma gondii detected. False negative results may occur in immunocompromised patients or if testing performed within 1 to 2 weeks of initial exposure and repeat testing may be helpful. A single negative result should not be used to rule-out toxoplasmosis, and repeat testing is recommended for patients at high risk for infection.

Borderline: Repeat testing on a new sample collected in 2 to 3 weeks is recommended to assess for seroconversion. Further confirmatory testing may be necessary at a Toxoplasma reference laboratory in borderline results persist following repeat testing.

Positive: Toxoplasma gondii IgM antibodies detected. Specimens with positive results should be confirmed by a laboratory with expertise in the diagnosis of toxoplasmosis. T gondii IgG antibodies detected, indicating recent or past infection. A significant change in T gondii IgG levels suggests recent infection. For confirmation of toxoplasmosis, the US Food and Drug Administration issued a Public Health Advisory (07/25/1997) that recommends sera found to be positive for T gondii IgM antibodies should be sent to a Toxoplasma reference laboratory.

Diagnosis of recent or active infection by Toxoplasma gondii can only be established based on a combination of clinical and serological data. The result of a single serum sample does not constitute sufficient proof for diagnosis of recent infection. Elevated IgM can persist from an acute infection that may have occurred as long ago as 1 year.

To differentiate between a recently acquired and past infection in patients who are IgM and IgG positive for Toxoplasma antibodies, Toxoplasma IgG avidity testing should be considered. A high avidity index for IgG antibodies indicates that the infection occurred at least 4 months ago. No clinical interpretation can be deduced from a low avidity result.

A negative Toxoplasma IgM result in combination with a positive IgG result does not completely rule out the possibility of an acute infection with Toxoplasma.

Elevated anti-IgM or IgG titers may be absent in patients who are immunocompromised. Results should be interpreted with caution in patients who are either HIV-positive, receiving immunosuppressive therapy, or have other disorders leading to immunosuppression.

A suspected diagnosis of central nervous system or congenital toxoplasmosis should be confirmed by detection of Toxoplasma gondii DNA by polymerase chain reaction (PCR) analysis of cerebrospinal fluid or amniotic fluid specimens, respectively (PTOX / Toxoplasma gondii, Molecular Detection, PCR, Varies).

If a serum specimen was collected too soon after infection, antibodies to T gondii may be absent. If this is suspected, a second serum specimen should be collected 2 to 3 weeks later, and the test repeated.

Heterophile antibodies in the patient specimens may interfere with IgM assay performance.

The performance of these assays has not been established for cord blood testing.

Specimens should not be collected from patients receiving therapy with high biotin doses (ie, >5 mg/day) until at least 8 hours following the last biotin administration.

As with any low prevalence analyte, there is the increased possibility that a positive result may be false, reducing the assay's positive predictive value. Per the Public Health Advisory (7/25/1997), the US Food and Drug Administration suggests that sera found to be positive for Toxoplasma gondii IgM antibodies should be submitted to a Toxoplasma reference laboratory.

Matta SK, Rinkenberger N, Dunay IR, Sibley LD. Toxoplasma gondii infection and its implications within the central nervous system. Nat Rev Microbiol. 2021;19(7):467-480. doi:10.1038/s41579-021

The electrochemiluminescence immunoassay for the in vitro qualitative determination of IgM antibodies to Toxoplasma gondii in human serum is a micro-capture test principle. During the first incubation, 6 mcL of sample are automatically prediluted 1:20 with Diluent Universal. T gondii-specific recombinant antigen labeled with a ruthenium complexa is added. Anti-Toxo IgM antibodies present in the sample react with the ruthenium-labeled T gondii-specific recombinant antigen. In the second incubation, biotinylated monoclonal h-IgM-specific antibodies and streptavidin-coated microparticles are added. The complex becomes bound to the solid phase via interaction of biotin and streptavidin. The reaction mixture is aspirated into the measuring cell where the microparticles are magnetically captured onto the surface of the electrode. Unbound substances are then removed with ProCell II M. Application of a voltage to the electrode then induces chemiluminescent emission which is measured by a photomultiplier. Results are determined automatically by the software by comparing the electrochemiluminescence signal obtained from the reaction product of the sample with the signal of the cutoff value previously obtained by calibration.(Package insert: Elecsys Toxo IgM, Roche Diagnostics. GmbH, 01/2024)

The electrochemiluminescence immunoassay for the in vitro quantitative determination of IgG antibodies to Toxoplasma gondii in human serum is a sandwich test principle. During the first incubation, 6 mcL of sample a biotinylated recombinant T gondii-specific antigen labeled with a ruthenium complex form a sandwich complex. In the second incubation, streptavidin-coated microparticles are added and the complex becomes bound to the solid phase via interaction of biotin and streptavidin. The reaction mixture is aspirated into the measuring cell where the microparticles are magnetically captured onto the surface of the electrode. Unbound substances are then removed with ProCell II M. Application of a voltage to the electrode then induces chemiluminescent emission which is measured by a photomultiplier. Results are determined by a calibration curve which is instrument-specifically generated by 2-point calibration and a master curve provided via the cobas link.(Package insert: Elecsys Toxo IgG, Roche Diagnostics. GmbH, 02/2022)

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This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

86778-Toxoplasma IgM

86777-Toxoplasma IgG