- PURPOSE : To examine the link between anticardiolipin antibodies and the features of antiphospholipid syndrome in patients with systemic lupus erythematosus (SLE). PATIENTS AND METHODS : In this prospective cohort study conducted in a single center, 390 SLE patients were followed up between June 1991 and 1994. At each assessment, a complete history, physical examination, and laboratory evaluation (including measurement of anticardiolipin antibodies) were performed according to a standard protocol. RESULTS : Forty-seven percent of the patients had an elevated level of anticardiolipin antibodies. In the univariate analysis, elevated anticardiolipin antibody levels were found to correlate with thrombocytopenia (P = 0.006), prolonged activated partial thromboplastin time (aPTT) (P = 0.003), and positive direct and indirect Coombs' test result's (P <0.001). No correlation was identified with any of the clinical features of antiphospholipid syndrome. In the multivariate analysis, anticardiolipin antibodies remained highly associated with thrombocytopenia (odds ratio [OR] 4.05, P = 0.02), positive direct Coombs' test (OR 2.31, P <0.001), and prolonged aPTT (OR 1.73, P = 0.03). In the multivariate model using venous/arterial thrombosis as the outcome variable, only prolonged aPTT was associated with venous/arterial thrombosis (OR 7.9, P <0.001). None of the laboratory variables were found to correlate with fetal loss. CONCLUSIONS : The presence of anticardiolipin antibodies in patients with SLE is associated with prolonged aPTT, thrombocytopenia, and positive Coombs' test result, but not with antiphospholipid syndrome. Prolonged aPTT is strongly associated with venous/arterial thrombosis.