Anticardiolipin antibody determination: comparison of three ELISA assays

The aim of this study was to compare two commercial kits (A and B) with our our own assay (C) for the determination of anticardiolipin antibodies (aCL). In 42 controls no subject was found to be aCL positive with kit A, seven were aCL positive with kit B and 1 with assay C. In 61 patients, the results were as follows: 50.8% aCL positivity for A, 57.4% for B and 50.8% for C. Only 57.3% of the patients were either positive (20 patients) or negative (15 patients) in the three tests. As for controls the concordance in patients was better between kit A and assay C than between kit B and assay C. Another group of patients with high IgM blank values in assay C were selected; when their blank values as measured with the kits were subtracted, 40% of the aCL positive patients with kit A became negative. In summary this comparison indicates that aCL positivity may vary according to the assay used and that non-specific binding may lead to false positive results.