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Sự thiếu hụt protein tổng số S và S protein không bị ràng buộc (phổ biến hơn) có thể dẫn đến một nhà nước hypercoagulable. Giống như thiếu protein C, nguy cơ huyết khối tăng mười lần, với nguy cơ cho các tàu sân bay 0,9-3,5% / năm. Protein S thiếu hụt chủ yếu là nguyên nhân gây huyết khối tĩnh mạch | 124 Hemostasis and Thrombosis Protein S is a cofactor for Protein C. Protein S exists both in bound and unbound form. Deficiencies of total protein S and of unbound protein S more common can lead to a hypercoagulable state. Like protein C deficiency the risk of thrombosis is increased ten fold with the risk for carriers 0.9- 3.5 year. Protein S deficiency primarily causes venous thrombosis. Antithrombin inhibits activated clotting factors. Deficiency of antithrombin primarily causes venous thrombosis and may increase the risk of thrombosis up to 30 fold. Lack of antithrombin is usually not associated with heparin resistance. Dysfibrinogenemia is a state in which defective fibrinogen molecules form clots which are difficult to degrade by fibrinolytic agents. Dysfibrinogenemia can be associated with both venous and arterial thrombosis. Due to the difficulty with thrombus formation some patients with dysfibrinogenemia may also have a bleeding diathesis. Factor VIII There is now convincing evidence implicating high levels of factor VIII 150 in venous thrombosis with a relative risk of 3 and high risk of recurrence. Mechanism of the factor VIII elevation is unknown but may be a combination of genetic factors and acquired risk factors such as inflammation. Lipoprotein a is a lipoprotein with uncertain function. High levels of lipoprotein a increase the risk of arteriosclerosis. The role of high levels of lipoprotein a in venous thrombosis remains controversial. Fibrinolytic disorders in theory should be classic causes of hypercoagulable states. However the role of defects in fibrinolytic enzymes in congenital hyperco-agulable states is controversial. No convincing relationship has been shown between defects in fibrinolysis and inherited hypercoagulable states. Suggested Evaluation in Patients with Venous Thrombosis The patient with venous thrombosis suspected of having a hypercoagulable state should be screened for diseases listed in Table 17.3. Table 17.3. Evaluation of