Beta-2 glycoprotein 1 (beta-2 GP1, also called apolipoprotein H) is a 326-amino acid polypeptide synthesized by hepatocytes, endothelial cells, and trophoblast cells.. Beta-2-Glycoprotein 1 (also known as apolipoprotein H), is a cofactor in antiphospholipid antibody binding and is the critical antigen in the antiphospholipid antibody syndrome. The presence of high titer IgG/IgM beta-2-glycoprotein 1 antibodies is one criteria for the diagnosis of antiphospholipid antibody syndrome.. Apolipoprotein H (Apo-H), previously known as β 2-glycoprotein I and beta-2 glycoprotein I, is a 38 kDa multifunctional apolipoprotein that in humans is encoded by the APOH gene . The β2-Glycoprotein I IgM test is a chemiluminescent immunoassay (CLIA), for use on IDS automated analyzers. It is used for the quantitative determination of the specific IgM antibodies directed against β2-glycoprotein I in human samples of serum or plasma (EDTA and Heparin).. The antiphospholipid syndrome (APS) is a systemic autoimmune disorder characterized by the main clinical features of venous and/or arterial thrombosis (intravascular blood clotting), thrombocytopenia, recurrent fetal loss, and moderate-to-high titers of antiphospholipid (aPL) antibodies, lupus anticoagulant, anti-cardiolipin antibodies . Strongly positive results for beta-2 glycoprotein 1 (beta-2 GP1) antibodies (>40 U/mL for IgG and/or IgM) are diagnostic criterion for antiphospholipid syndrome (APS). Lesser levels of beta-2 GP1 antibodies and antibodies of the IgA isotype may occur in patients with clinical signs of APS, but the results are not considered diagnostic. Beta-2 GP1 antibodies must be detected on 2 or more .