Value of autoantibodies to β2-glycoprotein 1 in the diagnosis of antiphospholipid syndrome

Objectives. To define the specificity and positive predictive value of anti-beta(2)-glycoprotein 1 (anti-beta(2)GP1) antibodies for the diagnosis of antiphospholipid syndrome (APS). Methods. We determined the presence of anticardiolipin (aCL) antibodies and anti-beta(2)-glycoprotein 1 (anti-beta(2)GP1) immunoglobulin (Ig) G and IgM in 191 consecutive sera from 191 patients and reviewed clinical data separately. aCL IgG and IgM were detected separately using commercial ELISA kits. Anti-beta(2)GP1 antibodies were detected with an in-house ELISA using beta2GP1. Results. Seven patients were diagnosed as having APS and 184 as having other diseases. Thirty-six patients were aCL-positive and 12 Were anti-beta(2)GP1-positive, seven of these 12 were APS patients. The specificity for anti-beta(2)GP1 in our population was 97% with a positive predictive value (PPV) of 58%. Among the aCL-positive patients, specificity was 90% and PPV 70-87%. Conclusions. This study shows that anti-beta(2)GP1 antibodies have a higher specificity and PPV than aCL for APS. The PPV of anti-beta(2)GP1 was greater in aCL-positive than in all patients. We conclude that screening for anti-p2GPI antibodies in aCL-positive patients increases the specificity and the PPV of aCL testing. In addition, We show that there is no need to screen for anti-beta(2)GP1 antibodies in the absence of aCL antibodies and in the absence of strong clinical suspicion of APS.