Lupus anticoagulant: revival of an old phenomenon.

The term lupus anticoagulant (LAC) refers to antiphospholipid antibodies assessed by means of phospholipid-dependent coagulation tests. About two-thirds of LAC-positive patients described in the literature have systemic lupus erythematosus (SLE) or a lupus-like syndrome. The estimated prevalence in SLE is about 30%. LAC is a marker of a subset of patients characterized by a high prevalence of thromboembolic complications (present in 40% of the LAC-positive patients), fetal loss (related to placental infarction), thrombocytopenia, biologically false positive tests for syphilis, antinuclear antibodies and a positive Coombs' test. There is a strong correlation between the presence of LAC and antibodies to the phospholipid cardiolipin, which can be estimated with relatively simple solid phase assays. Studies demonstrating in some patients interactions between LAC and either humoral factors with important functions in the (patho-) physiology of thrombosis, endothelial cells or platelets strongly suggest that LAC represents autoantibodies with pathogenic significance.