hematology and oncology
Antiphospholipid Syndrome (APS)
Introduction
Antiphospholipid syndrome is an autoimmune disorder characterized by venous and arterial thrombosis or pregnancy complications (eg, recurrent miscarriage) and persistent autoantibodies to phospholipid-bound proteins. The pathophysiology is not precisely known. Diagnosis is by blood tests. Anticoagulation is often used for prevention and treatment. (See also Overview of Thrombotic Disorders .) The antiphospholipid syndrome (APS) is an Autoimmune Disorders that is characterized by arterial, venous, or microvascular thrombosis or recurrent pregnancy loss caused by antibodies directed against one or more phospholipid-bound proteins (eg, beta-2 glycoprotein 1, prothrombin, annexin A5). In the clinical laboratory, antiphospholipid syndrome is associated with anticardiolipin antibodies, beta-2 glycoprotein 1 antibodies, and the lupus anticoagulant (or lupus inhibitor) which causes prolongation of phospholipid-dependent coagulation assays such as the PTT or dilute Russell viper venom time (dRVVT). The antibodies that cause prolongation of coagulation tests were originally called lupus anticoagulants because they were initially identified in patients with systemic lupus erythematosus (SLE). However, this terminology is no longer used because these antibodies can also occur in patients without SLE (as occurs in primary APS). The pathogenesis of thrombosis in APS is unclear. Beta-2 glycoprotein 1 in plasma binds to phospholipid-rich surfaces. Antibodies to beta-2 glycoprotein 1 upregulate cellular adhesion proteins, such as E selectin, and procoagulant proteins, such as tissue factor. Tissue factor is a receptor and cofactor for factor VII and is expressed on epithelial cells to help form a hemostatic barrier. In addition, antibodies to beta-2 glycoprotein 1 downregulate expression of tissue factor pathway inhibitor, an endogenous anticoagulant protein. Antiphospholipid antibodies also activate neutrophils and monocytes, which activate tissue factor, as well as platelets and complement. Each of these derangements may contribute to the hypercoagulable state associated with antiphospholipid syndrome. Clinical manifestations of APS include Overview of Thrombotic Disorders , 