Role of anti-β 2 glycoprotein 1 antibodies in ESRD patients with antiphospholipid antibody syndrome

Introduction. End stage renal disorder (ESRD) patients with antiphospholipid antibody syndrome (APAS) are at high risk for the development of post-transplant renal thrombosis. Positive titre of anticardiolipin antibodies (ACA) is considered a major characteristic of APAS. However, several studies have suggested that ACA in patients with APAS do not bind to phospholipids alone. Beta 2 glycoprotein 1 (beta2gp1), a 40-kD plasma protein is required. In this study, we have tested a hypothesis that significant portions of our ESRD patients with APAS have antibodies only to beta2gp1. Methods: Serum samples from each of 169 ESRD patients waiting for cadaver renal transplant in August 2000 were tested for ACA and anti-beta 2gp1 antibodies by enzyme-linked immunoabsorbent assay (ELISA) method. Twenty-four of these patients had clotting disorders that met the criteria established by the Eighth International Symposium on Antiphospholipid Antibodies (8). They included frequent areterio-venous (a-v) shunt thrombosis, cerebrovascular thrombosis, lupus, frequent abortions and microrenal angiopathy. Results: Thirty-three of the patients (20%) had positive titre of either ACA or beta2gp1 or both. Twenty-eight patients had ACA antibodies, of which eight had no evidence of clotting disorder while remaining 20 patients had various clotting disorders. Fourteen of these 20 patients with APAS had the positive titre of ACA only; the remaining six patients had both the antibodies, i.e. anti-beta2gp1 as well as ACA. There were four patients with APAS that had positive titres of only beta2gp1 antibodies. In total there were 11 patients with beta2gp1 antibodies, 10 of which had APAS, the remaining one did not. The sensitivity and the specificity of ACA test were 83 and 94%, respectively, and the sensitivity and specificity of beta2gp1 antibody test were 71 and 99%, respectively. The chi-square analysis demonstrated that there was statistically significant correlation between positive titres of both the antibodies and the presence of APAS. Conclusion: The APAS in the ESRD patients should be characterized by not only the positive titre of ACA but also the positive titres of anti-beta2gp1 antibodies in association with history of clotting disorder.