Reference values for thrombotic markers in children.

Thromboembolic events are an increasingly common problem encountered in children. The laboratory diagnosis of thrombotic disorders in children differs from that in adults. To establish the normal reference of natural anticoagulant parameters in children of different age groups, plasma from healthy children between the ages of 2 months and 16 years (n = 127) and adults (n = 30) were assayed for a disintegrin-like and metalloprotease with thrombospondin type 1 domain 13 (ADAMTS-13), von Willebrand factor collagen-binding activity (vWF:CB), tissue factor pathway inhibitor (TFPI), homocyteine and natural anticoagulants. Children were divided into four age groups: less than 1 year, 1-5 years, 6-10 years, and 11-16 years. The reference values for ADAMTS 13, homocysteine, and protein C activity were significantly lower in children of all age groups compared with those in the adults. Similarly, those for protein C antigen, total protein S, free protein S and antithrombin III (AT III) for children less than 1 year were significantly lower than in the adults. On the contrary, TFPI levels were significantly higher in the children for all age groups when compared with the adults. vWF:CB levels were comparable across all groups. There are age-related physiologic differences in ADAMTS-13, TFPI, homocysteine and natural anticoagulants between children and adults. Our data will provide physicians with a useful reference guide in interpreting test results of inhibitors of hemostatic parameters in children suspected of thrombotic disorders.