Risk factors for thromboembolism may be genetic and acquired (Table 88–1).
Hereditary thrombophilia is a genetically determined increased risk of thrombosis.
Up to 50% 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 88–2).
Up to 16% 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.
TABLE 88–1THROMBOPHILIAS AND PREDISPOSING RISK FACTORS FOR VENOUS THROMBOEMBOLISM |Favorite Table|Download (.pdf) TABLE 88–1 THROMBOPHILIAS AND PREDISPOSING RISK FACTORS FOR VENOUS THROMBOEMBOLISM
|Thrombophilias ||Acquired Predisposing Risk Factors for Venous Thrombosis |
|Common ||Increasing age |
|Factor V Leiden ||Surgery or trauma |
|Prothrombin G20210A ||Prolonged immobilization |
|Increased factor VIII level* ||Obesity |
|Homozygous C677T polymorphism in methylenetetrahydrofolate reductase† ||Smoking |
| ||Malignant neoplasms |
|Rare ||Myeloproliferative diseases |
|Protein C deficiency ||Superficial vein thrombosis |
|Protein S deficiency ||Previous venous thrombosis/varicose veins |
|Antithrombin deficiency ||Pregnancy and puerperium |
|Very rare ||Use of female hormones |
|Dysfibrinogenemia ||Antiphospholipid antibodies/lupus anticoagulants |
|Homozygous homocystinuria ||Hyperhomocysteinemia |
| ||Activated protein C resistance unrelated to factor V Leiden |
TABLE 88–2FREQUENCY OF THROMBOPHILIAS IN HEALTHY SUBJECTS AND UNSELECTED AND SELECTED PATIENTS WITH VENOUS THROMBOSIS |Favorite Table|Download (.pdf) TABLE 88–2 FREQUENCY OF THROMBOPHILIAS IN HEALTHY SUBJECTS AND UNSELECTED AND SELECTED PATIENTS WITH VENOUS THROMBOSIS
|Type of Thrombophilia ||Healthy Subjects (% affected) ||Unselected Subjects (% affected) ||Selected Subjects (% affected) |
|Factor V Leiden ||5* ||19 ||40 |
| ||0.05† || || |
|Prothrombin G20210A ||3* ||7 ||16 |
| ||0.06† || || |
|Protein C deficiency ||0.03 ||4 ||5 |
|Protein S deficiency ||0.18 ||2 ||4 |
|Antithrombin deficiency ||0.02 ||2 ||4 |
HEREDITARY RESISTANCE TO ACTIVATED PROTEIN C
Etiology and Pathogenesis
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