Developmental hemostasis: laboratory and clinical implications.

The pediatric hemostatic balance, which is different from that in adults, is an evolving process as the hemostatic system changes and matures throughout the time from fetal to adult life, particularly in the first months of life. The concept of developmental hemostasis was confirmed by several studies evaluating different patients' population in various technical conditions. All these studies demonstrated that, at birth, the plasma levels of most coagulation factors were around half that found in adults, the preterm newborns having lower levels than full-term newborns. Adult values were usually reached between a few months of age and up to above 16 years for specific parameters. If the global trends are consistent across the studies, differences in absolute values could be demonstrated that are likely due to differences in the reagents and/or the instruments used. Accordingly, it is recommended by the Perinatal and Pediatric Haemostasis Subcommittee of the Scientific and Standardization Committee of the ISTH for each laboratory to define the age-dependent reference ranges using its own technical condition. The understanding of that concept of developmental hemostasis, which is now universally accepted, is critical to ensure optimal prevention, diagnosis, and treatment of thrombotic and hemorrhagic diseases in children. Actually, developmental hemostasis could affect the interaction between anticoagulant drugs and the coagulation system and so explain in part the discrepancy between anticoagulation in adults and in children. Finally, developmental hemostasis could probably provide a protective mechanism for neonates and children, contributing to the decreased risk of thrombosis and/or bleeding in these age-groups.