Evaluation of the fibrinolytic system in full-term neonates

Plasminogen activity and antigen, euglobulin fibrinolytic activity, tissue-type plasminogen activator activity and antigen urokinase-type plasminogen activator antigen, plasminogen activator inhibitor-1 activity and antigen, plasminogen activator inhibitor-2 antigen, tissue-type plasminogen activator/plasminogen activator inhibitor complexes, alpha 2-antiplasmin, histidine-rich glycoprotein, and fibrinogen/fibrin degradation products were measured in blood samples taken from the umbilical vein of 100 healthy full-term newborns. Results were compared with a control group of 30 healthy adults. The overall fibrinolytic activity assessed on fibrin plates was significantly increased (P < 0.002). We also observed high tissue-type plasminogen activator activity levels (P < 0.001), whereas urokinase-type plasminogen activator antigen levels were lower than in adults. There was a significant reduction in plasminogen activity and antigen (P < 0.0001), plasminogen activator inhibitor-1 activity (P < 0.05), alpha 2-antiplasmin (P < 0.0001), and histidine-rich glycoprotein (P < 0.0001), whereas plasminogen activator inhibitor-2, tissue-type plasminogen activator/plasminogen activator inhibitor complexes and fibrinogen/fibrin degradation products did not differ between groups. We conclude that in the newborn there is increased fibrinolytic activity, mainly due to increased plasminogen activators and reduced fibrinolysis inhibition, without systemic fibrinolysis and fibrinogenolysis.