Factors That Predict Risk of Thrombosis in Relatives of Patients With Unprovoked Venous Thromboembolism

Background: Factors that predict the risk of venous thromboembolism in the first-degree relatives of patients with unprovoked venous thromboembolism are uncertain but important for counseling. We aimed to identify risk factors for, and quantify the risk of, venous thromboembolism in first-degree relatives of patients (index case patients) with a first episode of unprovoked venous thromboembolism. Methods: In a cross-sectional study, using a standardized method and without knowledge of whether patients or their relatives had thrombophilia, we assessed the prevalence of previous venous thromboembolism in 1,916 first-degree relatives of 378 unselected patients with a first episode of unprovoked venous thromboembolism. Patient characteristics, and the presence of, factor V Leiden or the G20210A prothrombin gene mutation in patients, were assessed as predictors of venous thromboembolism in patient's relatives. Results: There were 1.02 previous episodes of venous thromboembolism in the first-degree relatives (prevalence, 5.3%). Thrombosis at a young age in patients was the strongest predictor of venous thromboembolism in relatives, with an adjusted odds ratio (OR) for younger patients (ie, patients < 45 years of age when venous thromboembolism occurred; lowest quartile) compared with older patients (ie, patients > 71),cars of age; highest quartile) of 3.27 (95% CI, 1.68 to 6.38). The presence of factor V Leiden or the G20210A prothrombin gene in patients was a weak independent predictor or venous thromboembolism in relatives (adjusted OR, 1.48; 95% CI, 0.64 to 2.33). Conclusion: Unprovoked venous thromboembolisin at a young age is associated with a substantially increased risk of venous thromboembolism in patients' families. (CHEST 2009; 136:1537-1545)