Prothrombotic conditions in an unselected cohort of children with venous thromboembolic disease 1 1 Presented in part at the 43rd Annual meeting, The American Society of Hematology, Orlando, FL, December 2001.

Venous thromboembolic events (VTEs) in children are usually associated with underlying clinical conditions. The added contribution of prothrombotic conditions to the occurrence of VTEs in children is not clear. This study reports the prevalence of prothrombotic conditions in 171 consecutive children with VTE followed in the Hospital for Sick Children Thrombosis Outpatient Clinic. The median age of the children at the time of VTE was 2.3 months (range 1 day to 16.5 years). An underlying medical condition and a central venous line (CVL) were present in 156 (91%) and 132 (77%) of 171 children, respectively. A positive family history was present in 8% of children. The prevalence of factor V Leiden was 4.7%, prothrombin G20210A polymorphism was 2.3%, protein S deficiency was 1.2%, protein C deficiency was 0.6% and increased plasma lipoprotein (a) concentration (>30 mg dL-1) was 7.5% (tested in 107 children). The overall frequency of inherited prothrombotic coagulation proteins was 13% (95% confidence interval 7 to 19%) and the frequency was not significantly different between neonates and older children with VTE. Inherited prothrombotic coagulation proteins were not associated with gender, CVL-related VTE, a positive family history of thrombosis or spontaneous VTE in neonates. Increased frequency of inherited prothrombotic coagulation proteins was, however, found in older children with spontaneous VTE (60%) compared with older children with VTEs secondary to an underlying medical condition (10%) (P = 0.02). In conclusion, this study indicates that inherited prothrombotic coagulation proteins do not contribute significantly to the pathogenesis of VTEs in neonates and children, in whom the most significant etiological factors are the presence of a CVL and/or other medical conditions.