Determining whether a patient has had previous exposure to or recent infection with Toxoplasma gondii
IgG is not useful for diagnosing infection in infants younger than 6 months of age. IgG antibodies in this age group usually are the result of passive transfer from the mother.
Detection of IgM-class antibodies to Toxoplasma gondii may be useful as a screen for recent infection with T gondii.
Per the US Food and Drug Administration, IgM-positive results by a screening assay should be confirmed, for example, by a Toxoplasma reference laboratory.
A single negative result by this assay does not rule-out toxoplasmosis as the specimen may have been collected too early following infection, prior to development of detectable antibodies.
A single IgG-positive result is indicative of exposure to T gondii at some time in the past.
| Test Id | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| TXM | Toxoplasma Ab, IgM, S | Yes | Yes |
| TOXGP | Toxoplasma Ab, IgG, S | Yes | Yes |
Multiplex Flow Immunoassay (MFI)
T. gondii
Toxoplasma gondii
Toxoplasma IgG & IgM Antibody Assays
Toxoplasma, IgG Antibody, Serum
Toxoplasma, IgM Antibody, Serum
Toxoplasmosis
Serum
Collection Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container/Tube: Aliquot tube
Specimen Volume: 1.5 mL
Collection Instructions: Centrifuge and aliquot serum into a plastic vial.
If not ordering electronically, complete, print, and send Infectious Disease Serology Test Request (T916) with the specimen.
0.8 mL
| Gross hemolysis | Reject |
| Gross lipemia | Reject |
| Heat-inactivated specimen | Reject |
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum | Refrigerated (preferred) | 14 days | |
| Frozen | 14 days |
Determining whether a patient has had previous exposure to or recent infection with Toxoplasma gondii
IgG is not useful for diagnosing infection in infants younger than 6 months of age. IgG antibodies in this age group usually are the result of passive transfer from the mother.
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.(1) 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 between the ages of 12 and 49 have antibodies to T gondii.(2)
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.(3)
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.(4) 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.
Toxoplasma IgM
Negative
Toxoplasma IgG
Negative
Toxoplasma IgG Value
< or =9 IU/mL (Negative)
10-11 IU/mL (Equivocal)
> or =12 IU/mL (Positive)
Reference values apply to all ages.
Active toxoplasmosis is suggested by the presence of IgM-class antibodies, but elevated anti-IgM titers may be absent in patients who are immunocompromised. 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 polymerase chain reaction (PCR) analysis of cerebrospinal fluid or amniotic fluid specimens (PTOX / Toxoplasma gondii, Molecular Detection, PCR, Varies).
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.
A single negative result should not be used to rule-out toxoplasmosis, and repeat testing is recommended for patients at high risk for infection.
IgG is only indicative of previous exposure to Toxoplasma (recent or past). A single positive Toxoplasma IgG result should not be used to diagnose recent infection. Seroconversion from negative to positive IgG is indicative of recent T gondii infection.
Diagnosis of recent infection by Toxoplasma gondii can only be established by a combination of clinical and serological data.
The result of a single serum specimen does not constitute sufficient proof for diagnosis of recent infection. If a serum specimen was collected too soon after infection, IgM 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.
Sera collected very early during the acute stage of infection may have Toxoplasma IgG levels below 9 IU/mL. The Toxoplasma IgG assay should not be used alone to diagnose recent T gondii infection. Results should be considered in conjunction with clinical presentation, patient history, and other laboratory findings.
Results should be interpreted with caution in patients who are either HIV-positive, receiving immunosuppressive therapy, or have other disorders leading to immunosuppression.
Heterophile antibodies in the patient specimens may interfere with the assay performance.
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 (07/25/1997), the US Food and Drug Administration suggests that sera found to be positive for T gondii IgM antibodies should be submitted to a Toxoplasma reference laboratory.
The performance characteristics of this assay have not been evaluated in immunocompromised individuals and have not been established for cord blood or for testing of neonates.
1. Tenter AM, Heckeroth AR, Weiss LM: Toxoplasma gondii: from animals to humans. Int J Parasitol. 2000 Nov;30(12-13):1217-1258
2. Jones JL, Kruszon-Moran D, Rivera HN, Price C, Wilkins PP: Toxoplasma gondii seroprevalence in the United States 2009-2010 and comparison with the past two decades. Am J Trop Med Hyg. 2014 Jun;90(6):1135-1139
3. Luft BJ, Remington JS: Toxoplasmic encephalitis in AIDS. Clin Infect Dis. 1992 Aug;15(2):211-222
4. Wong SY, Remington JS: Toxoplasmosis in pregnancy. Clin Infect Dis. 1994 Jun;18(6):853-861
5. Wang ZD, Liu HH, Ma ZX, et al: Toxoplasma gondii infection in immunocompromised patients: A systematic review and meta-analysis. Front Microbiol. 2017 Mar 9;8:389
The BioPlex 2200 Toxoplasma gondii IgM and IgG assays use multiplex flow immunoassay technology. Briefly, Toxoplasma antigen-coated fluorescent beads are mixed with an aliquot of patient sample and sample diluent and then incubated at 37 degrees C. During this time, IgM and IgG anti-Toxoplasma antibodies in the specimen will bind to the Toxoplasma antigen on the beads. After a wash cycle, a fluorescently-labeled antihuman IgM- and IgG-antibody conjugate is added to the mixture and incubated at 37 degrees C. Following a wash step to remove unbound conjugate, the bead mixture is passed through a detector that identifies the bead based on dye fluorescence and determines the amount of antibody captured by the antigen based on fluorescence of the antihuman-IgG conjugate. Raw data is calculated in relative fluorescence intensity and is converted to an antibody index for interpretation for IgM and an IU/mL for IgG.
Three additional dyed beads: an internal standard bead, a serum verification bead, and a reagent black bead are present in each reaction mixture to verify detector response, the addition of serum to the reaction vessel, and the absence of significant nonspecific binding in serum, respectively.(Package inserts: BioPlex 2200 System, ToRC IgG and ToRC IgM. Bio-Rad Laboratories; 03/2012 and 08/2017)
Monday through Saturday
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
| Test Id | Test Order Name | Order LOINC Value |
|---|---|---|
| TXMGP | Toxoplasma Ab, IgM and IgG, S | 88746-3 |
| Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
|---|---|---|
| TOXG | Toxoplasma Ab, IgG, S | 40677-7 |
| DEXG6 | Toxoplasma IgG Value | 8039-0 |
| TXM | Toxoplasma Ab, IgM, S | 40678-5 |