The coagulation system in children: developmental and pathophysiological considerations

The coagulation system in children is complex and ever changing, a fact encapsulated in the term developmental hemostasis. Studies confirm that there are quantitative and almost certainly qualitative differences in the coagulation system with age, and the control of these changes comes from something external to the liver. What remains uncertain is the magnitude of the qualitative changes and the implications of the changes for the growing child. At the very least, developmental hemostasis probably provides a protective mechanism for neonates and children and hence contributes to the decreased risk of thromboembolic and/or hemorrhagic events in these age groups. In addition, developmental hemostasis could also reflect the role that hemostatic proteins play in physiological development and hence the demand of other processes, such as angiogenesis. Finally, without doubt, developmental hemostasis affects the interactions of anticoagulant drugs with the coagulation system. This article will initially discuss the most recent evidence with respect to qualitative age-related changes in the coagulation system. Subsequently the article will discuss the coagulation system during childhood in light of the three aforementioned areas of clinical impact and suggest possible strategies to further understand this complex and exciting field of study.