Commercial Laboratory IgM Testing for Toxoplasma gondii in Pregnancy: A 20‐Year Experience

Abstract

OBJECTIVE: This study was performed to review the clinical utility of commercial laboratory Toxoplasmosis-specific IgM testing during pregnancy and outcomes of the gestation at our institution. METHODS: A retrospective review of all women referred for suspected acute Toxoplasma gondii infection during pregnancy from 1984 through 2004 was performed. Women were diagnosed with suspected acute toxoplasmosis based on commercial laboratory serologic antibody testing. All women had blood sent to a recognized reference laboratory for antibody testing within 2 weeks of the commercial laboratory results. The study protocol was approved by the Institutional Review Board. Chi-square analysis were used with a significance of P < .05. RESULTS: A total of 130 women were evaluated during the study period with 116 IgM positive results from the commercial laboratories. The commercial laboratory antibodies were as follows: IgM positive with IgG negative (n = 20), IgM positive with IgG positive (n = 96), and IgM negative with IgG positive (n = 14). There was a significant reduction in the IgM positive results when comparing commercial laboratory (n = 116) with the reference laboratory results (n = 28; p < .001). Acute toxoplasmosis infection was diagnosed in 7 (5%) of the women. All cases of acute toxoplasmosis infection had a positive commercial laboratory IgM result. The false positive rate for the commercial laboratory IgM was 88.6% and the diagnostic indices were sensitivity 100%, specificity 11.4%, positive predictive value 6% and negative predictive value 100%. CONCLUSION: Commercial laboratory Toxoplasmosis-specific IgM is associated with a high false positive rate. The commercial and reference laboratory IgM results identified all cases of acute toxoplasmosis infection. Commercial laboratories reflexively obtaining reference laboratory confirmation of positive results could reduce costs associated with testing, referrals, retesting, and invasive procedures.

Seroprevalence and risk factors of Toxoplasma gondii infection among pregnant women in Trinidad and Tobago

“…However, this is an unlikely scenario because in the longitudinal component of this study, with a total of 116 women sampled at each of the three trimesters or during each of the first and second trimesters, 22 (19.0%) were seropositive for IgM for the first time during their pregnancies. It is pertinent, however, to mention that one cannot always equate the detection of T. gondii-specific IgM to acute infection since commercial test kits have yielded false-positives (41). Although cats are the primary source of oocysts that cause human and livestock infections (3,5,30), in our study, household cats or handling of cat litter were not found to be signif- icantly associated with T. gondii infection in pregnant women.…”

Significance of a Positive Toxoplasma Immunoglobulin M Test Result in the United States

“…A lack of avidity test in the study by Liesenfeld may also have resulted in a higher proportion of acute infection diagnoses. In a study on the clinical utility of positive IgM test results in pregnant women obtained at their NRLs, Garry et al found the IgM test to have a very low PPV (6%) for an acute infection when their serum underwent confirmatory testing at PAMF-TSL (13). Furthermore, the sensitivity, specificity, PPV, and negative predictive value (NPV) of PAMF-TSL IgM ELISA in their study were 100%, 83%, 25%, and 100%, respectively.…”

LDBio-Toxo II Immunoglobulin G Western Blot Confirmatory Test for Anti- Toxoplasma Antibody Detection

“…However, some immunoenzymatic tests detecting anti-Toxoplasma IgM antibodies seem to have low positive predictive values and can yield discrepant results (7,9,17,19). Therefore, seroconversion is often confirmed only once IgG is detected (5,9,13).…”