Lupus anticoagulant: clinical significance in anticardiolipin positive patients with systemic lupus erythematosus.

The significance of anticardiolipin antibodies and the lupus anticoagulant was studied in 58 consecutive patients with systemic lupus erythematosus. On 85 occasions serum IgG and IgM anticardiolipin antibodies were measured by an enzyme linked immunosorbent assay (ELISA), and simultaneous plasma samples tested for lupus anticoagulant activity. The most significant association with clinical events (previous thrombosis or thrombocytopenia occurring in 11/58 patients) was with prolonged tissue thromboplastin inhibition time (TTIT) followed by prolonged kaolin cephalin clotting time (KCCT) then raised IgG anticardiolipin antibody concentrations and dilute Russell's viper venom time. Although IgG anticardiolipin antibodies or KCCT were the most sensitive tests in identifying this group, the TTIT was the most specific (98%). Nine patients were IgG anticardiolipin antibody positive and lupus anticoagulant negative, of whom one had thrombocytopenia but none had thrombosis. The presence of a lupus anticoagulant in anticardiolipin antibody positive patients increases specificity for certain adverse clinical events.