CLINICAL OBSERVATIONS, INTERVENTIONS, AND THERAPEUTIC TRIALS Risk of recurrent venous thrombosis in children with combined prothrombotic risk factors

After a first episode of spontaneous venous thromboembolism (VTE), the risk of recurrence persists for many years. However, comprehensive data about the risk of recurrence in pediatric patients have hitherto not been reported. Thus, this study evaluated the risk of recurrent VTE among children in relation to the presence of single or combined-inherited and/or acquired causes of thrombophilia. A total of 301 patients aged neonate to 18 years (median, 6 years) who were referred for an objectively confirmed first episode of spontaneous VTE were followed prospectively for a median time of 7 years (range, 6 months to 15 years) after withdrawal of anticoagulation. All patients were studied for established acquired and inherited causes of thromboembolism. With reference to all 301 patients, one single prothrombotic risk factor was found in 176 subjects (58.5%), whereas combined defects were found in 20.6% (n 5 62). Recurrent VTE occurred in 64 patients (21.3%) within a median time of 3.5 years (range, 7 weeks to 15 years) after withdrawal of anticoagulation, with a significantly shorter cumulative thrombosis-free survival in children carrying combined defects (P < .0001; chi-square, 42.2). The factor V G1691A mutation was present in the majority of patients with recurrent VTE. Including genetic defects, gender, and acquired risk factors, multivariate analysis showed that only the presence of prothrombotic defects increases the risk of recurrent VTE (single defect: odds ratio [OR], 4.6; 95% confidence interval [CI], 2.3-9.0; P < .0001; combined defect: OR, 24.0; 95% CI: 5.3108.7; P < .0001). As a consequence of the data presented here, it is suggested that screening for genetic risk factors be done among pediatric patients with VTE. (Blood. 2001;97:858-862)