Role of ABO blood group and of other risk factors on the presence of residual vein obstruction after deep-vein thrombosis.

The presence of residual vein obstruction (RVO) has been consistently associated with an increased risk of post-thrombotic syndrome in patients with a previous deep vein thrombosis (DVT) and there is some evidence suggesting an increased risk of DVT recurrence. Only few studies have assessed potential risk factors for RVO. In this study, we evaluated whether ABO blood group with or without associated thrombophilic abnormalities is associated with RVO after a standard course of anticoagulation for a first DVT. Patients with a first DVT who underwent screening for thrombophilic abnormalities were eligible for this study. Information was collected on ABO blood group and on risk factors for DVT. Each patient underwent compression ultrasonography of the lower limbs for the detection of RVO at least 6months after a standard course of anticoagulant treatment. A total of 268 patients (mean age 50.3years, 120 women) were included. After 8.3±2.9months of anticoagulant treatment, 126 (47.0%) patients had RVO. At multivariate analysis, active malignancy (Odds Ratios [OR] 5.54, 95% confidence interval [CI] 2.17, 14.13), non-O blood group (OR 3.71, 95% CI 1.61, 8.56), and femoral involvement (OR 3.35 95% CI 1.94, 5.78) were significantly associated with RVO whereas an unprovoked index event was only marginally significant (OR 1.81 95% CI 0.98, 3.36 p 0.06) and severe thrombophilia was not associated with RVO (OR 1.32 95% CI 0.56, 3.11). After a standard course of anticoagulation for a first DVT, patients with non-O blood group are at increased risk of RVO.