Lupus anticoagulants in patients with systemic lupus erythematosus

Lupus anticoagulants (LA) and anticardiolipin antibodies (aCL) are known as thrombosis-related antiphospholipid antibodies. LA is not as well characterized as aCL, and the relation between LA and aCL is not clarified. Since standardized method for the detection of LA has not been established, we measured LA activities in outpatients with SLE by using two different methods (KCT and dRVVT), and analyzed the characteristics of LA in SLE. LA was detected in 29.8% of all samples (14.3% in both methods, 15.5% in one method). IgG-aCL and IgM-aCL was detected in 38% and 20%, respectively, of all LA positive samples. Though a good correlation was observed between LA activities and IgG-aCL levels, a considerable number of LA positive samples were negative for aCL. This indicated the presence of factors with LA activity other than aCL. On the contrary there was also a high percentage of LA negative samples with positive aCL (42.4% in IgG-aCL, 47.4% in IgM-aCL), suggesting the presence of aCL with poor or low LA activity. These findings showed the heterogeneity of antiphospholipid antibodies both in LA and in aCL. The platelet function tests showed increased platelet adhesiveness and normal platelet aggregation in LA positive patients with SLE even in the inactive phase. The serum levels of factors such as protein C, protein S, antithrombin III and thrombomodulin were within normal range. Clinical features such as hemolytic anemia, thrombosis and abortion were more frequently observed in LA positive population than in LA negative population. The clinical features tend to be different between patients with dRVVT-LA and those with KCT-LA, though not significant. Because of the heterogeneity in LA, a combination of more than two different methods including dRVVT was recommended for the detection and the evaluation of LA.