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Test ID: TXM    
Toxoplasma gondii Antibody, IgM, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Detection of recent infection with Toxoplasma gondii

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Toxoplasma gondii is an obligate intracellular protozoan parasite that is 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, Toxoplasma gondii can remain latent for the life of the host; the risk for reactivation is highest among immunosuppressed individuals.

 

Seroprevalence studies performed in the United States indicate that approximately 6.7% of individuals between the ages of 12 and 49 have antibodies to Toxoplasma gondii.

 

Infection of immunocompetent adults is typically asymptomatic. In symptomatic cases, patients most commonly 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 involved 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. A majority of 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.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Negative

Reference values apply to all ages.

Interpretation Provides information to assist in interpretation of the test results

Active toxoplasmosis is suggested by the presence of IgM-class antibodies, but elevated anti-IgM titers may be absent in immunocompromised patients. In addition, elevated IgM can persist from an acute infection that may have occurred as long ago as 1 year. A suspected diagnosis of acute toxoplasmosis should be confirmed by detection of Toxoplasma gondii DNA by PCR analysis of cerebrospinal fluid or amniotic fluid specimens (PTOX / Toxoplasma gondii, Molecular Detection, PCR).

 

For confirmation of toxoplasmosis, the FDA issued a Public Health Advisory (7/25/1997) that recommends that sera found to be positive for Toxoplasma gondii IgM antibodies should be sent to a Toxoplasma reference laboratory.

 

A single negative result should not be used to rule-out toxoplasmosis and repeat testing is recommended for patients at high risk for infection.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Diagnosis of recent infection by Toxoplasma gondii can only be established on the basis of a combination of clinical and serological data.

 

The result of a single serum sample does not constitute sufficient proof for diagnosis of recent infection.

 

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

 

Results should be interpreted with caution in HIV-positive patients, patients receiving immunosuppressive therapy, or individuals with other disorders leading to immunosuppression.

 

Heterophile antibodies in the patient samples may interfere with the assay performance.

 

The performance of the assay has not been established for cord blood testing.

 

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

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Tenter AM, Heckeroth AR, Weiss LM: Toxoplasma gondii: from animals to humans. Int J Parasitol 2000;30(12-13):1217-1258

2. Jones JL, Kruszon-Moran D, Rivera HN, et al: Toxoplasma gondii seroprevalence in the United States 2009-2010 and comparison with the past two decades. Am J Trop Med Hyg. 2014;90(6):1135-1139

3. Wang ZD, Liu, HH, Ma ZX, et al: Toxoplasma gondii infection in immunocompromised patients: A systematic review and Meta-Analysis. Front Microbiol. 2017;8:389

4. Wong SY, Remington JS: Toxoplasmosis in pregnancy. Clin Infect Dis 1994;18(6):853-861