Clinical significance and correlations between anti-β2 glycoprotein I IgA assays in antiphospholipid syndrome and/or systemic lupus erythematosus.

Background: The objective of this investigation was to examine the clinical significance of IgA anti-β2 glycoprotein I (anti-β2GPI) antibodies and the inter-assay relationships between kits for their determination.

Methods: Serum samples from 269 patients with clinical diagnoses of systemic lupus erythematosus (SLE) and/or antiphospholipid syndrome (APS), individuals positive for antiphospholipid antibodies (aPL) with or without APS or SLE, and 182 controls were tested for anti-β2GPI IgA antibodies using kits from four manufacturers.

Results: The positivity rates for the different IgA anti-β2GPI antibody kits varied in the disease groups; 7.8-14.7% (SLE only), 12.0-15.7% (SLE and APS/aPL), 14.7-58.8% (APS only), and 17.4-52.2% (aPL only). Kappa agreements between any 2 kits within disease groups were also variable and ranged from 0.25-1.00 (SLE), 0.18-1.00 (SLE and APS/aPL), 0.22-0.94 (APS only), and 0.32-0.91 (aPL only). Univariate analyses also showed variable relative risks for specific APS clinical manifestations with the different kits evaluated. Overall, diagnostic and predictive values for IgA anti-β2GPI antibodies are kit-dependent; therefore results are not interchangeable. While all 4 kits seem able to predict venous thrombosis tolerably well, there was a variable performance in predicting pregnancy related morbidity.

Conclusions: Efforts to standardize these assays are highly needed prior to their formal adoption in routine clinical evaluation.