Comparative analysis of Quanta Lite and Euroimmun enzyme-linked immunosorbent assays for the determination of antiphospholipid antibodies

Objectives: Despite the large number of published studies and guidelines for determining antiphospholipid antibodies (aPLs), laboratory results can be contradictory, depending on the test used and the clinical data. This study aimed to investigate the agreement of antibody positivity between the commercial enzyme-linked immunosorbent assay (ELISA) kits from Quanta Lite and Euroimmun, to evaluate the analytical and clinical performance of the aPLs, and to compare the cutoff calculated by the laboratory with the manufacturer’s cutoff values. Methods: This study included 79 patients with primary antiphospholipid syndrome (APS), 47 patients with APS associated with systemic lupus erythematosus, and 56 healthy individuals. The immunoglobulin (Ig) G/IgM isotypes of anti-cardiolipin (aCL) and anti-β2-glycoprotein I (aβ2GPI) were determined in all serum samples. Results: We found that there was a significant difference between the manufacturer’s and calculated cutoff values for aβ2GPI IgG and IgM in terms of the number of patients identified as positive ( P < 0.001), but that there was no difference between the manufacturer’s and calculated cutoff values for aCL IgG and IgM. Using the manufacturer’s cutoff values, we found substantial agreement for aCL IgG (Kappa = 0.712) and aβ2GPI IgG (Kappa = 0.761), moderate agreement for aCL IgM (Kappa = 0.474), while fair agreement was found for aβ2GPI IgM (Kappa = 0.329), comparing the ELISA kits analysed. Using the calculated cutoff, we found substantial agreement for aCL IgG (Kappa = 0.712) and moderate agreement for aβ2GPI IgG (Kappa = 0.533) and aβ2GPI IgM (Kappa = 0.424), while fair agreement was found for aCL IgM (Kappa = 0.339). Conclusion: Our results indicate the need for further standardization of ELISA tests for the determination of aPLs, particularly in terms of selecting appropriate cutoff values.