Summary
The physiologic mechanisms that protect children from thromboembolic complications
are not known. We investigated the regulation of thrombin in children because of its
central importance to thrombosis. The capacity to generate thrombin in vitro (chromogenic
assay) was decreased by 26% in plasmas from children (1-16 yrs; n = 102) compared
to adults ([20-45 yrs; n = 20; p <0.001]). The addition of purified prothrombin to
plasmas from children increased thrombin generation to adult values. The capacity
of plasmas to inhibit 125I-α-thrombin was increased by 21% in children compared to adults (p = 0.020), with
significantly more thrombin complexed to a2-macroglobulin (α2M) in children.
When DVT occur in children, adult guidelines for heparin therapy are used. At low
heparin concentrations (0.1 and 0.2 U/ml), thrombin generation was decreased by 30%
in children compared to adults (p <0.001). At high heparin levels (0.4 U/ml), thrombin
generation was negligible in all plasmas. ATIII inhibited over 95% of thrombin in
all plasmas in the presence of heparin.
In summary, thrombin regulation differs in children from adults and may protect children
from thromboembolic complications. When DVT do occur, heparin requirements may differ
in children compared to adults.
