Evaluation of the Bio-Rad BioPlex 2200 IgM Multiplex Flow Immunoassay.

Background: Toxoplasmosis is routinely diagnosed through detection of -specific antibodies. However, the imperfect specificity of serologic assays is a well-recognized limitation. The new BioPlex 2200 (Bio-Rad Laboratories) , rubella, and cytomegalovirus (ToRC) IgM multiplex flow immunoassay (MFI) received FDA clearance in May 2017. We evaluated the clinical performance of the new IgM and existing IgG portion of this MFI.

Methods: Three hundred prospectively collected consecutive, residual sera, submitted for serologic testing as part of routine clinical care, and an archived set of 52 residual sera previously positive for anti- IgM and IgG with the predicate ADVIA Centaur IgM and IgG assays (Siemens) were evaluated. Performance of the BioPlex 2200 IgM and IgG MFIs was assessed by calculating positive (PPA) and negative percent agreement (NPA) compared to the Centaur tests.

Results: Among prospective specimens, the BioPlex 2200 IgM and IgG MFIs demonstrated a PPA of 0% (0/7) and 82.3% (28/34) and NPA of 99.3% (288/290) and 95.8% (251/262), respectively, with the Centaur assays. Chart review of the 7 Centaur IgM-positive samples revealed that these were likely falsely positive. Among archived samples, the BioPlex 2200 IM and IgG MFIs showed PPAs of 90.4% (47/52) and 100% (52/52), respectively.

Conclusions: The BioPlex 2200 IgM and IgG MFIs demonstrated excellent concordance with the Centaur assays. The IgM MFI may provide higher specificity in low-prevalence populations.