ABSTRACT
Antiphospholipid antibodies are a heterogeneous group of autoantibodies directed against phospholipids (principally of negative charge), phospholipids bound to proteins (β2glycoprotein I, prothrombin, annexin V, protein C or protein S) or both. They are responsible for the false-positive serological tests for syphilis, the lupus anticoagulant (LA) as well as the anticardiolipin antibodies and against other phospholipids (e.g. phosphatidylserine, phosphatidylethanolamine). In common clinical practice, the best known antiphospholipid antibodies are LA, anticardiolipin antibodies and the antibodies to (β2-glycoprotein I. LA was first described by Conley and Hartman in 1952, and is an autoantibody that prolongs clotting times in vitro. It is detected by means of coagulation assays. Results are either positive or negative, and therefore cannot be quantified. The antibodies to cardiolipin (immunoglobulin (Ig) G or IgM) as well as (β2-glycoprotein I are detected by enzyme-linked immunosorbent assay (ELISA). Anticardiolipin antibody levels are quantified in GPL (IgG) or MPL (IgM) units. The LA and/or anticardiolipin antibodies are the only two antiphospholipid antibodies necessary for diagnosis. Nevertheless, both must always be determined, because only 50% of patients with antiphospholipid syndrome (APLS) have both types of antibody.
