Performance characteristics of a commercial antibody-capture enzyme immunoassay for detection of Toxoplasma-specific IgM antibodies

Performance characteristics of six IMMULITE 2000 TORCH assays

TORCH is an acronym for Toxoplasma gondii (Toxo), other microorganisms (eg, syphilis), rubella virus (RV), cytomegalovirus (CMV), and herpes simplex virus (HSV) that are associated with congenital abnormalities from maternal infection. We evaluated linearity, imprecision, and comparison with commercially available methods of the IMMULITE 2000 (Diagnostic Products, Los Angeles, CA) Toxo IgG, Toxo IgM, RV IgG, RV IgM, CMV IgG, and HSV IgG assays. Linearity and imprecision results were acceptable. The IMMULITE 2000 assays show good concordance with other commercially available methods except for Toxo IgM and RV IgM. Toxo IgM showed better concordance with a consensus of 3 of 4 (Access, Beckman Coulter, Fullerton, CA; IMMULITE 2000; Platelia, Bio-Rad Laboratories Diagnostics Group, Redmond, WA; and Vidas, bioMerieux, Hazelwood, MO) assays than with Access alone. The RV IgM assay showed better concordance with the Zeus method than with the Diamedix method (Diamedix, Miami, FL). The IMMULITE 2000 TORCH assays studied show acceptable performance and are suitable for routine clinical use. Some commercial assays for Toxo IgM and RV IgM show rather poor concordance.

Prospective study of IgM to Toxoplasma gondii on Beckman Coulter's Access(TM) immunoassay system and comparison with Zeus ELISA and gull IFA assays

We compared a new assay for Toxoplasma IgM on the Access analyzer (Beckman Coulter, Inc., Chaska, MN, USA), a random access instrument based on the principle of paramagnetic particle enzyme immunoassay with an enzyme-linked immunosorbent assay (ELISA) (Zeus Scientific, Inc., Raritan, NJ, USA) and an immunofluorescent assay (IFA) (Gull Laboratories, Inc., Salt Lake City, UT, USA). Four hundred fresh, unfrozen clinical samples from pregnant women (n = 154), HIV positive patients (n = 41), and patients in whom infection with Toxoplasma gondii was suspected (n = 200) were collected and assayed over a three month period. The specificity of the Access assay was compared to the consensus results. Results that were discrepant between the ELISA and IFA were resolved using a third IFA (Zeus). Once resolved, the specificity for the Access assay, the Zeus ELISA and the Gull IFA were 99.22%, 97.91%, and 99.45%, respectively. We conclude that the Access assay specificity is comparable to consensus results, minimizing false positive results; and because it is a random access instrument, it may be preferable over batch methods.

Detection of immunoglobulin G (IgG) and IgM antibodies to Toxoplasma gondii: evaluation of four commercial immunoassay systems

A comparative evaluation of the following commercial immunoassays for the determination of antibodies to Toxoplasma gondii was performed: Behring Diagnostics OPUS Toxo G and Toxo M, Abbott Diagnostics IMX Toxo-IgG 2.0 and Toxo-IgM, Sanofi Diagnostics Pasteur Platelia Toxo IgG and Toxo IgM, and bioMérieux Vitek VIDAS Toxo IgG and IgM. Of 676 specimens that were tested for Toxoplasma-specific immunoglobulin G (IgG) antibodies, 26% were reactive by all methods while 8% displayed some discrepancy. Of 718 specimens that were tested for Toxoplasma-specific IgM antibodies, 3% were reactive by all methods while 10% displayed some discrepancy. Analysis of discrepant specimens revealed performance shortcomings with all IgM-specific assays. The impact of such shortcomings is magnified in a population with a low prevalence of toxoplasmosis.

Multicenter evaluation of a new commercial assay for detection of immunoglobulin M antibodies to Toxoplasma gondii. Multicenter Study Group

A new commercial assay for detection of IgM-specific antibodies to Toxoplasma gondii (IMx Toxo IgM, Abbott, USA), based on microparticle enzyme immunoassay technology, was evaluated at 15 clinical sites in Europe and the USA. Performance characteristics were established by testing clinical specimens collected randomly from pregnant women, blood donors, individuals with suspected Toxoplasma gondii infection and individuals confirmed HIV positive. Reference testing was performed using Toxo-M EIA (Abbott). Specimens evaluated at European sites yielding discordant results between the new assay and the reference EIA were further tested with an immunosorbent agglutination assay; at sites in the USA, discordant results were resolved using Platelia Toxo IgM (Sanofi, France) and Vidas Toxo IgM (bioMérieux, France) assays. In addition, matched plasma and serum, heat-treated and non-heat-treated specimens, and fresh and frozen specimens were evaluated at the USA sites. At European sites the new commercial assay had a sensitivity of 95.6% (196/205), a specificity of 99.8% (3,137/3,143) and an agreement of 99.6% (3,333/3,348) following resolution of discordant results; sensitivity in the USA was 97.4% (184/189), specificity was 99.8% (1,204/1,207) and agreement was 99.4% (1,388/1,396) following resolution. The new IMx Toxo IgM is a sensitive and specific assay for measurement of IgM antibodies to Toxoplasma gondii in human serum and plasma.