A b s t r a c t Venous thromboembolism (VTE) results from the interaction of the Virchow triad (venous stasis, endothelial injury, and hypercoagulability). Risk factors for increased hypercoagulability, or thrombophilia, include activated protein C resistance/factor V Leiden, the prothrombin G20210A mutation, deficiencies of the natural anticoagulants (antithrombin, proteins C and S), antiphospholipid antibodies, hyperhomocysteinemia, and increased factor VIII activity. Not all patients with

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... need to be tested for such risk factors, but patients with thrombophilia should be evaluated for all possibilities to better estimate risk. At the same time, testing should be patient-specific because assay results are affected by preanalytic variables, including thrombosis and anticoagulant therapy.