Bioplex 2200 multiplex

IgG and IgM isotypes of anti-B2GPI and anti-CL were determined by addressable laser bead immunoassay (ALBIA) using BioPLex 2200 multiplex immunoassay system APLS (Bio-Rad, Hercules CA, USA). The cutoff to consider IgG and IgM anti-B2GPI and anti-CL as positive was 18 U/mL, according to the 99th percentile evaluated in a healthy population. LA was measured in a sample of 67 patients using HemosiL dRVVT (cutoff ratio 1.2) and HemosiL Silica Clotting Time (cut-off ratio 1.3) assays (Instrumentation Laboratory SpA, Milano, Italy).

Autoantibodies were measured in pre-transplant serum used for crossmatch or in a serum sample obtained in the month before transplantation. Anti-cardiolipin or anti-B2GPI of IgG and IgM isotypes were evaluated using the BioPLex 2200 multiplex immunoassay system (Biorad, Hercules CA, USA). Antibody levels above 18 U/mL were considered positive (99th percentile of healthy population).
IgA aCL and aBGPI antibodies were quantified by enzyme-linked immunosorbent assays (ELISA) using IgA-aCL and IgA-aB2GPI QUANTA Lite (INOVA Diagnostics Inc., San Diego, CA, USA). Antibody levels above 20 U/mL were considered positive. Cutoff were established with the 99th percentile of a healthy population in our hospital and coincided with the cutoff suggested in the assay manufacturer's guidelines (25 (link)).
Mean levels of anticardiolipin antibodies were: IgG 1.9 ± 0.2 and IgM 1.7 ± 0.3 IU/ml. Antibodies anti-B2GPI mean levels were: IgG 2.0 ± 0.4 IU/ml and IgM 1.8 ± 0.4 IU/ml. No significant differences were observed between the percentage of patients who were positive for anti-cardiolipin or anti-B2GPI (IgG/IgM isotypes) vs. healthy people. No association was found between the presence of IgG/IgM aPL and post-transplant mortality.