The prolongation of the thrombotest clotting time in newborns.

As judged from thrombotest dilution curves clotting inhibiting material was present in 67% of human umbilical cord plasma samples of healthy full term infants (n = 40). The correlation coefficient (r-value) between the thrombotest clotting times and the prothrombin levels was -0.46. Using sensitive enzyme immuno assays for fibrin degradation products (FbDP) and fibrinogen degradation products (FgDP), we found that no degradation products could be demonstrated in the non-inhibited group whereas small amounts of these products were present in the inhibited group. These small amounts were undetectable using conventional assays. The most striking finding was the presence of fibrin and fibrinogen degradation products. The prolongation of the thrombotest clotting time could be imitated by adding fibrinogen fragment X to umbilical cord plasma in which no clotting inhibiting material was present in the thrombotest dilution curve. We conclude that the thrombotest clotting is of limited value in the assessment of the vitamin K-dependent coagulation factors in umbilical cord plasma. As utmost care was taken to avoid proteolytic breakdown in vitro, our findings most likely reflect an enhanced fibrino(geno)lytic activity in umbilical cord plasma in vivo.