Comprehensive evaluation of antiphospholipid antibody testing methodologies in APS diagnosis: performance comparisons across assay systems and clinical subtypes

OBJECTIVES: Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by thrombosis and obstetric complications associated with antiphospholipid antibodies (aPLs). This study aimed to compare the diagnostic performance of six commercial assay systems for detecting aCL and aβ2GPI antibodies. METHODS: Sixty-three APS patients, 50 SLE patients, 67 disease controls, and 62 healthy controls were enrolled. aCL and aβ2GPI antibodies of IgA, IgG, and IgM isotypes were measured using six commercial platforms, including three ELISA-based systems and three CLIA-based systems. Inter-assay concordance was compared across all detection platforms, and ROC curve analysis was performed to evaluate and compare their diagnostic performance in APS. RESULTS: Inter-assay concordance varied across platforms, with IgG isotypes showing the highest consistency and IgA exhibiting the lowest agreement. Overall, CLIA-based systems demonstrated superior classification performance compared to ELISA-based methods. The highest area under the curve (AUC) reached 0.811, with sensitivity and specificity up to 0.730 and 0.891, respectively. IgG isotypes demonstrated the best overall performance, while IgA and IgM showed greater variability. The inclusion of IgA modestly improved sensitivity in some systems, although this was sometimes accompanied by decreased specificity. LA-positive patients had higher aPL positivity rates than LA-negative ones, and aPL levels were higher in thrombotic vs. obstetric APS. CONCLUSIONS: Significant variability exists among commercial aPL detection systems. CLIA-based methods provided better consistency and diagnostic accuracy than ELISA. The inclusion of IgA provided additional diagnostic value in identifying APS patients who tested negative for aCL and aβ2GPI of the IgG and IgM isotypes.