Performance of the BioPlex 2200 Flow Immunoassay in Critical Cases of Serodiagnosis of Toxoplasmosis

Abstract

The BioPlex 2200 automated analyzer (Bio-Rad Laboratories, Hercules, CA) is a recently developed multiplex analyzer that enables the detection of anti-Toxoplasma, -rubella, and -cytomegalovirus antibodies in the same assay. The aim of this study was to compare this new technology (using the BioPlex 2200 ToRC IgG/IgM kit) in critical cases of serodiagnosis of toxoplasmosis (acute, chronic, or congenital infections and cases with discrepant results) to the technologies used in our routine practice, i.e., the Platelia IgG/IgM enzyme-linked immunosorbent assays (ELISAs) (Bio-Rad Laboratories) and the Toxo-Screen direct agglutination assay (bioMérieux, Lyon, France). Overall, most cases of false-positive/negative results obtained with the Platelia IgG or Toxo-Screen assay were corrected by the BioPlex 2200 ToRC IgG (87.5%). Furthermore, the analysis of 35 sequences of sera showed a trend toward a more rapid decrease of IgM titers by BioPlex 2200 than by Platelia. These results for IgM detection can be explained by a weaker detection of residual IgM. Indeed, among 23 serum samples from patients with probable past infection with long-lasting IgM (Platelia M positive and IgG avidity index, >0.5), the BioPlex 2200 Toxoplasma IgM assay was positive for only 11 serum samples. In our panel of critical cases comprising 156 serum and 6 cord blood samples from 103 patients with acute, chronic, or congenital infection, the BioPlex 2200 IgG assay was a sensitive (97.8%) and specific (91.3%) method for IgG detection. The high specificity (97.4%) of IgM detection combined with the shorter kinetics of IgM titers may considerably reduce the number of residual IgM detections, thus yielding more precise diagnoses of acute infections. Infections due to the protozoan parasite Toxoplasma gondii are highly prevalent among humans and animals worldwide and are responsible for severe complications in immunocompromised patients and in children born to infected mothers. Diagnosis of this infection is therefore important not only for treatment but also for epidemiology and prevention (1). The use of serologic tests to search for anti-T. gondii antibodies is a primary method of diagnosis (2). Different commercial serologic tests are available and possess unique patterns of increases and decreases with time after infection (3-5). The tests most commonly used in routine laboratories for the detection of anti-T. gondii IgG are the doublesandwich enzyme-linked immunosorbent assay (ELISA), the indirect fluorescent-antibody assay (IFA), the indirect hemagglutination assay, and the direct agglutination test. For anti-T. gondii IgM, the most common tests are the double-sandwich ELISA, the immunosorbent agglutination assay (ISAGA), and the IFA. Nevertheless, these techniques have certain disadvantages, such as significant hands-on time or low throughput (6).The recently developed BioPlex 2200 automated analyzer (BioRad Laboratories) is a multiplex flow immunoassay (MFI) that enables the simultaneous detection and identification of multiple antibodies in ...

Serological and molecular rapid diagnostic tests for Toxoplasma infection in humans and animals

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