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INTRODUCTION

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  • Risk factors for thromboembolism may be genetic and acquired (Table 89–1).

  • Hereditary thrombophilia is a genetically determined increased risk of thrombosis.

  • Up to 50 percent of patients presenting with a first deep venous thrombosis will have an abnormal laboratory test suggesting a thrombophilic defect, and patients with recurrent thromboses or with a strong family history are even more likely to have laboratory evidence of a thrombophilic state (Table 89–2).

  • Up to 16 percent of patients with thrombophilia have inherited more than one abnormality.

  • These inherited defects also interact frequently with acquired risk factors, such as inactivity, trauma, malignancy, or oral contraceptive use, to lead to clinical thrombosis.

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Table Graphic Jump Location
TABLE 89–1THROMBOPHILIAS AND PREDISPOSING RISK FACTORS FOR VENOUS THROMBOEMBOLISM
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Table Graphic Jump Location
TABLE 89–2FREQUENCY OF THROMBOPHILIAS IN HEALTHY SUBJECTS AND UNSELECTED AND SELECTED PATIENTS WITH VENOUS THROMBOSIS
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HEREDITARY RESISTANCE TO ACTIVATED PROTEIN C (APC)

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Etiology and Pathogenesis

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  • APC resistance is an abnormally reduced anticoagulant response of a patient's plasma that, in more than 90 percent of cases, is caused by a genetic abnormality of factor V (substitution of glutamine for arginine at position 506), which significantly retards inactivation of factor Va by APC. The abnormal factor V is generally referred to as "factor V Leiden."

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