New insights into neonatal coagulation: normal clot formation despite lower intra-clot thrombin levels

BACKGROUND: Healthy neonates exhibit no bleeding tendencies, but exhibit longer partial thromboplastin times than adults. Lower clotting factor levels may be balanced by lower inhibitor levels, which is not reflected in routine coagulation assays, but could result in normal clot formation in vivo. The novel thrombodynamics assay simulates a damaged vessel with tissue factor immobilized to a surface. We hypothesized that intra-clot thrombin levels and spatial fibrin clot formation with this assay are comparable in neonates and adults. METHODS: Coagulation was tested in plasma from venous neonatal blood (N = 12), cord blood (N = 30), and adult blood (N = 20) using thrombodynamics and calibrated automated thrombography. RESULTS: Neonates exhibited a higher initial rate of dot formation than adults (adult: 60.7 +/- 3.9 mu m/min; neonatal: 66.8 +/- 3.9 mu m/min; cord: 68.1 +/- 3.3 mu m/min; P< 0.001) and a comparable stationary rate of clot formation (adult: 35.8 +/- 8.5 mu m/min; neonatal: 37.0 +/- 4.6 mu m/min; cord: 36.0 +/- 5.2 mu m/min; P = 0.834). Intra-clot thrombin levels were lower in neonates (adult: 41.9 +/- 11.2 AU/I; neonatal: 22.6 +/- 10.2 AU/I; cord: 23.6 +/- 9.7 AU/I; P < 0.001), but the longitudinal rate of thrombin propagation was comparable (adult: 27.2 +/- 4.2 mu m/min neonatal; 27.9 +/- 2.9 mu m/min; cord: 27.6 +/- 3.4 mu m/min; P = 0.862). CONCLUSIONS: Despite lower intra-clot thrombin levels, neonates exhibit normal spatial fibrin clot growth, which concurs with clinically well-functioning hemostasis in healthy neonates.