The incidence of venous thromboembolism in thrombophilic children: a prospective cohort study.

Antithrombin and protein C and S defects, factor V Leiden mutation, and G20210A prothrombin gene mutation are well-recognized risk factors for venous thromboembolism (VTE) in adults, especially during circumstantial situations such as trauma, immobilization, surgery, or oral contraceptive treatment. The relevance of these defects in predisposing children to VTE is still undefined. In a prospective cohort study we assessed the incidence of spontaneous and risk period-related VTE in asymptomatic children (aged 1-14 years), who were family members of a proband with an objectively diagnosed venous thromboembolic event and a documented single thrombophilic abnormality. We enrolled 143 children from 63 families. Of them, 81 (56.6%) were carriers of an inherited defect, whereas the remaining 62 were free from known genetic or acquired causes of thrombophilia. The mean observation period was 5 years (range, 1-8 years) in each group. Thirty-one risk periods occurred in the carriers group and 20 in noncarriers. Neither spontaneous nor risk period-related VTE occurred in either group during 395 and 296 observation years, respectively. However, circumstances where most of the pediatric thromboses occur (insertion of central venous lines, cancer, and cardiovascular surgery) were not encountered. In conclusion, the thrombotic risk in otherwise healthy children with a single identified thrombophilic defect appears to be very low. Common triggering conditions for VTE in thrombophilic adults do not seem to increase the thrombotic risk in children carrying the same inherited defect. Accordingly, screening for thrombophilia in otherwise healthy children younger than 15 years who belong to families with inherited defects predisposing to thrombosis seems unjustified.