Beta 2-Glycoprotein 1 Screen ELISA is a solid phase enzyme immunoassay employing native ß2-glycoprotein I highly purified from human plasma for the combined quantitative detection of IgA, IgG and IgM anti-bodies against ß2-glycoprotein I in human serum. Anti-ß2-glycoprotein I antibodies recognize specific epitopes on human ß2-glycoprotein I which are expressed only when ß2-glycoprotein I interacts with lipid membranes or when absorbed to other surfaces (e.g. microtiter plate). The assay is an aid in the diagnosis and risk of primary and secondary antiphospholipid syndrome (APS). Antibodies against ß2-glycoprotein I belong to the group of anti-phospholipid antibodies mainly targeted against complexes composed of negatively charged phospholipids (cardiolipin e.g) and plasma proteins like ß2- glycoprotein I, prothrombin, protein C or protein S. Reactivity against isolated ß2- glycoprotein I is found, too. Thus ß2-glycoprotein I is discussed to be an autoantigen on its own. ß2-glycoprotein I, also called apolipoprotein H, is a 50 kDa ß2 globuline which is associated in vivo with lipoprotein, platelets and phospholipids and which seems to inhibit the intrinsic coagulation pathway, the prothrombinase activity and the ADP-dependent platelet aggregation. Anti-phospholipid antibodies are frequently found in sera of patients with systemic lupus erythematosus and related diseases and are typical for the secondary development of an antiphospholipid syndrome (APS). Whilst, anti-phospholipid antibodies in patients with no other autoimmune diseases characterize a primary APS. Many studies have shown a correlation between these autoantibodies and an enhanced incidence of thrombosis, thrombocytopenia and habitual abortions (as a consequence of placental infarction). The exact mechanism how pathogenic anti-phospholipid antibodies induce thrombosis has not been revealed yet.