Detection of Antiphospholipid Antibodies Using a Novel Multiplex Test Method: Correlation with ELISA Methods.

-Background: Laboratory criteria for the antiphospholipid antibody syndrome (APS) include detection of the lupus anticoagulant (LA) by coagulation based tests, or detection of either anti-cardiolipin (aCL), or anti-B₂-glycoprotein I (aB2GPI) antibodies by enzyme-linked immunoabsorbant assay (ELISA). Multiplex testing enables simultaneous measurement of multiple serum antibodies with small beads coated with target antigens and small sample volumes (5 μL). We compared the concordance of a prototype multiplex method to standard ELISA methods for measuring IgG and IgM antibodies directed against CL or B₂GPI.

Methods: Samples from patients with suspected APS were tested for IgG and IgM aCL and aB₂GPI antibodies using standard ELISA methods (ELISA, Bio-Rad Laboratories, Hercules, CA) and by a prototype multiplex bead set analyzed on the BioPlex 2200 (Bio-Rad Laboratories, Hercules, CA). The multiplex method used beads coated with either CL alone, B₂GPI alone, or CL-B₂GPI complex. Results were normalized using ratios (obtained result/upper limit of normal). A positive result was defined as a ratio of > 1. For CL, the multiplex test is considered positive if positive results are present using beads with either the CL alone or the CL-B₂GPI complex.

Results:

Conclusions: The overall concordance of multiplex results with ELISA results was good (81–89%). Negative multiplex results showed excellent correlation with ELISA (85–93%). Positive multiplex results had variable correlation with ELISA (51–76%). Evaluation of clinically significant positive results and clinical outcome measures is needed to determine clinical sensitivity and specificity of the multiplex test. Further refinement of the multiplex platform may provide an efficient and cost-effective assay for antibodies associated with the antiphospholipid syndrome.