ABSTRACT
This chapter aims to provide a description of the many types of circulating anticoagulants that occur and to distinguish them from those more appropriately described as phospholipid-dependent or lupus anticoagulants. Anticoagulants may be categorized as either specific antibodies to clotting factors or nonspecific in their function. The former class can be split into slow- or fast-acting categories. Circulating anticoagulants interacting specifically with factor IX have been reported mainly in patients with hemophilia B. Although most reviews of the subject of circulating anticoagulants have concentrated on antibodies, there are now several reports of nonantibody mediated anticoagulants. Autoantibodies to factor VIII may occur in peripartum women, in patients with autoimmune disorders and in otherwise healthy elderly individuals and constitute a significant life-threatening hemorrhagic risk factor. The mechanism of factor VIII antibodies may serve as a useful model for studies still to be carried out with antibodies of unknown etiology.
