Do antibodies to β2-glycoprotein 1 contribute to the better characterization of the antiphospholipid syndrome?

Abstract

The aim of this study was to determine if the measurement of anti-β2-glycoprotein I antibodies (aβ2-GPI) in serum levels contributes to the better characterization of the clinical situation of patients with antiphospholipid syndrome (APS). For this purpose aβ2-GPI of both isotypes was measured in 42 patients with APS and 32 SLE patients without APS. Clinical records of all patients were thoroughly reviewed. The presence of aβ2-GPI was correlated with the clinical manifestations of APS and compared with the presence of anticardiolipin antibodies (aCL) and lupus anticoagulant (LA) activity. There was a positive correlation between levels of aCL and aβ2-GPI for both IgG and IgM isotypes (r of Spearman = 0.82 and 0.64 respectively, P = 0.0001). Both antibodies presented significantly higher titres in LA positive patients (P 0.05). The specificity for APS was 91% for IgG aβ2-GPI vs 75% for IgG aCL and 87% for IgM aβ2-GPI vs 81% for IgM aCL. 68% of patients with thrombosis of 100% of patients with thrombocytopenia showed positive tests for all three markers (aCL, LA, aβ2-GPI). Simultaneous presence of circulating LA and high titres of both aCL and aβ2-GPI identify a subset of patients with primary APS (PAPS) who have a more severe clinical course of the disease. Although the specificity of aβ2-GPI IgG is higher than that of aCL IgG, when all three tests are performed aβ2-GPI testing provides only additional information to that of aCL and LA. Therefore, we concluded that the aβ2-GPI test should not be considered as a substitute for conventional LA or aCL assays. However, performance of aβ2-GPI seems to be important in PAPS with high aCL titres, to alert the physician about the risk for the worst course of the illness.