Study of Abbott Toxo IMx system for detection of immunoglobulin G and immunoglobulin M toxoplasma antibodies: value of confirmatory testing for diagnosis of acute toxoplasmosis

Abstract

We compared the Abbott Toxo immunoglobulin G (IgG) and IgM IMx assays with the Sabin-Feldman dye test and an IgM enzyme-linked immunosorbent assay (ELISA) in 398 serum samples previously tested in our laboratory (retrospective group) and 1,000 consecutive serum samples, tested as they were received in our laboratory in 1995 (prospective group). In the retrospective group, the IgG IMx had a sensitivity of 100%, specificity of 99.0%, positive predictive value of 99.0%, negative predictive value of 100%, and overall agreement of 99.5%. The percentages for the IgM IMx were 97.8, 99.0, 98.9, 98, and 98.4%, respectively. In the prospective group, the IgG IMx had a sensitivity of 97.8%, specificity of 98.7%, positive predictive value of 97.8%, negative predictive value of 98.7%, and overall agreement of 98.4%. The percentages for the IgM IMx were 88.3, 95.9, 74.7, 98.3, and 95%. A serological profile (IgA and IgE antibodies and the differential agglutination [AC/HS] test) was performed in an attempt to resolve discrepancies. Of 21 serum samples that were positive in the IgM IMx and negative in the IgM ELISA, 19 had serological profiles which were most compatible with an infection acquired in the distant past. Of 8 serum samples which were positive in the IgM ELISA and negative in the IgM IMx, 5 had serological profiles which were most compatible with an infection acquired in the distant past. Of the 55 serum samples that were positive in both IgM tests, 21 were from patients who had serological profiles which were most compatible with an infection acquired in the distant past. In conclusion, our data highlight the importance of confirmatory testing for the diagnosis of recently acquired infection with Toxoplasma gondii. When compared with the dye test and IgM ELISA, the Toxo IgG and IgM IMx assays, respectively, revealed high overall agreement in the retrospective and prospective study.

False-positive results in immunoglobulin M (IgM) toxoplasma antibody tests and importance of confirmatory testing: the Platelia Toxo IgM test

“…Only rarely has the accuracy of new assays been evaluated in studies in which both large numbers of preselected sera and routine sera were used (Table 3). Using the latter approach, Joynson et al (13) and our group (15) have shown that the accuracy of tests differs markedly depending on the use of selected or routine sera. Thus, because most reports in the literature do not reflect the overall accuracy of these tests, the actual numbers of false-positive results might be underestimated.…”

Recombinant Antigens To DetectToxoplasma gondii-Specific Immunoglobulin G and Immunoglobulin M in Human Sera by Enzyme Immunoassay

“…Since a number of the serological targets for the detection of T. gondii antibodies are sequestered within internal organelles, the method of preparation of the tachyzoite antigen has a significant effect on assay performance, as shown by the differential agglutination assay (6). Hence, it is not surprising that commercial tests that employ the tachyzoite antigen to detect serum antibodies exhibit interassay variation (14,19,28,29,53,59).…”

“…The enzyme-linked immunosorbent assay (ELISA) for the detection of immunoglobulins is one of the easiest tests to perform, and many manual and automated serologic tests for the detection of T. gondii-specific immunoglobulin G (IgG) and IgM are commercially available. The currently available tests for the detection of IgG and IgM antibodies in infected individuals vary in their ability to detect serum antibodies (14,19,28,29,53,59). The differences observed between these serologic tests is probably due in part to the various preparations of antigen used to detect serum antibody.…”

Intravenous Immunoglobulin Therapy: Confounding Effects on Serological Screening for Toxoplasmosis during Pregnancy

“…However, the serological pattern (the IgG titers and the absence of IgM) and the high anti-Toxoplasma IgG avidity (the index was 0.55 for the serum collected on 30 October) for the two positive sera strongly suggested that the infection had been acquired before pregnancy (7). Even though the absence of detectable specific IgM is highly compatible with an infection acquired in the distant past, it must be emphasized that even the presence of IgM would not have been an absolute proof of a recent infection (6). Three hypotheses could thus be put forward: (i) there was a true infection with a very unusual serological profile (which could pose quite a challenge to the interpretation of other cases); (ii) there had been an error in the serum identification (this was controlled many times, and no mistake was evidenced); or (iii) immune disorders in the patient could have led to the presence of unusual antibody subsets (which could perhaps explain discrepancies in serology and IgG avidity).…”