hematology and oncology
Coagulation Disorders Caused by Circulating Anticoagulants
Introduction
Circulating anticoagulants are usually autoantibodies that neutralize specific clotting factors in vivo (eg, an autoantibody against factor VIII or factor V) or inhibit phospholipid-bound proteins in vitro (antiphospholipid antibodies). Occasionally, the latter type of autoantibody causes bleeding by binding in vivo to prothrombin-phospholipid complexes. (See also Overview of Coagulation Disorders .) Circulating anticoagulants should be suspected in patients with Excessive Bleeding combined with either a prolonged partial thromboplastin time (PTT) or prothrombin time (PT) that does not correct when the test is repeated with a 1:1 mixture of normal plasma and the patient’s plasma. Autoantibodies directed against protein/phospholipid complexes typically cause arterial and/or venous thrombosis (the Antiphospholipid Syndrome (APS) [APS]). The precise pathophysiology of thrombosis in APS is unknown. Although the protein-phospholipid autoantibodies frequently bind beta2-glycoprotein-1, it is unclear how this interaction triggers thrombosis. In a subset of patients, the autoantibodies bind to prothrombin-phospholipid complexes and induce hypoprothrombinemia and bleeding. 