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Thrombosis, defined as excessive clotting, has three main causes: reduced blood flow (stasis), increase in blood coagulation factors (hypercoagulability), and abnormalities in the vessel wall. Once the endothelium is injured, platelet adhesion is accompanied by platelet aggregation and thrombin formation. This process is usually tightly regulated in order to prevent excessive bleeding or clotting. However, at times, the process is uncontrolled, and a thrombus can form in excessive amounts or in an unusual place, causing harm.

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Thrombosis and thrombophilia in childhood is of increasing concern. Although symptomatic thrombotic disease in children is rare when compared with adults, its occurrence can lead to mortality or life-long sequelae. The reported rate of thrombosis is 5.3 per 10,000 hospitalized patients, with a bimodal peak in incidence in the neonatal and adolescent age groups.1-4 Less than 10% of events in children are idiopathic.1-4 Thrombosis during childhood is a multifactorial event caused by both genetic and acquired risk factors. Three or 4 different thrombotic risk factors are identified in most cases.1,4,5,6 Most children with thrombosis have an underlying medical condition that alters the hemostatic system to induce activation of coagulation and/or to prevent the inhibition of coagulation. The majority of conditions are related to inflammation or to abnormal blood flow (Table 438-1). In addition to the hemostatic changes secondary to underlying illness, many children also have the additional risk factor of a central venous catheter inserted to facilitate therapy for the underlying illness.1-3,7,8 The use of central venous catheter constitutes the most common acquired risk factor for thrombosis.5,7,8 As many as 60% of children with thrombosis will also have an inherited prothrombotic abnormality (Table 438-2), but the clinical relevance of congenital thrombophilia in asymptomatic children or in the presence of an acquired risk factor (eg, the presence of a central venous catheter) in childhood is still uncertain.1,9,10 There is debate about which children to screen, as well as when and how, for these genetic states. Families should be counseled about the significance of a prothrombotic state before testing is performed, especially in asymptomatic children. The pediatric community needs to be able to educate families about the signs and symptoms of thromboembolic disease, medical treatments and their potential adverse effects, and types of inherited and acquired thrombophilias.

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Table 438-1. Major Medical Illnesses Associated with Thromboembolic Complications
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Table 438-2. Inherited and Acquired Thrombophilia

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