THE PROLONGATION OF THE THROMBOTEST CLOTTING TIME IN NEWBORNS

Abstract

We investigated 40 human umbilical cord plasma samples of healthy full term infants. The samples were drawn under conditions which minimize in vitro activation of the haemostatic mechanism. In 67% clotting inhibiting material was present as judged from thrombotest dilution curves. The prothrombin (factor II) clotting activity (one stage method) ranged from 28 to 74% (mean value 50.6% ± 12.1). The correlation coefficient between the thrombotest clotting times and theprothrombin levels was -0.46. Using sensitive immuno assays for fibrin degradation products (XDP) and fibrinogen degradation products (FDP) based on monoclonal antibodies, we found that no degradation products could be demonstrated in the non-inhibited group (in the thrombotest dilution curves) 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 small amounts of purified degradation product fragment X to umbilical cord plasma with a normal thrombotest clotting time. The thrombotest clotting time is often used in clinical practice to obtain an impression of the levels of the vitamin K-dependent coagulation factors. We conclude that the thrombotest clotting time is of limited value in the assessment of the vitamin K-dependent coagulation factors in umbilical cord plasma because in 67% of the cases a further ("false") prolongation of the thrombotest clotting time is caused by small amounts of fibrin(ogen) degradation products. 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.