Coagulation, Anticoagulation, and Fibrinolysis

Background A subset of hemostatic disorders are due to an imbalance in coagulation or fibrinolysis. Disorders of coagulation or fibrinolysis can be either inherited (e.g., hemophilia A) or acquired (e.g., liver disease), and the clinical presentation is typically either bleeding or thrombosis. Laboratory testing is used to diagnose and to monitor the therapy of patients with these disorders. Additionally, a growing list of anticoagulant medications need laboratory testing to adjust the dose or to assess the risk for bleeding or thrombosis. Content This chapter describes laboratory testing for disorders of coagulation and fibrinolysis. Prothrombin time (PT), activated partial thromboplastin time (aPTT), thrombin time, and fibrinogen are routine tests in coagulation laboratories and are used in the initial evaluation of bleeding or thrombosis. Mixing studies and specialized testing of the coagulation and fibrinolytic pathways are used in an algorithmic fashion to complete the diagnostic workup. d-Dimer testing is a marker of fibrinolysis used to assess disseminated intravascular coagulation or to exclude venous thromboembolism (VTE). Thrombotic disorders may be investigated with protein C, protein S, antithrombin, factor V Leiden (FVL) mutation, prothrombin G20210A mutation, and lupus anticoagulant (LAC) tests. Laboratory testing of patients on a variety of anticoagulant medications are also described.