SummaryExtrinsic coagulation pathway inhibitor may be an important regulator of haemostasis to prevent thrombosis after tissue damage. The functional activity of this inhibitor was determined using a chromogenic substrate assay, and compared to the activities of anti thrombin, heparin cofactor II and protein C during the perioperative period of elective hip replacement (n = 28), cholecystectomy (n = 11), and vascular surgery (n = 5). Peroperatively, all the inhibitors decreased rather similarly and to the same degree as the decrease in albumin concentration. The decreases during hip surgery were about 2-fold the decreases observed during cholecystectomy. A significant peroperative increase in extrinsic pathway inhibitor activity was observed in vascular surgery, probably due to a bolus injection of heparin. Antithrombin, heparin cofactor II and protein C levels normalized on days 3-5 postoperatively in all three patient groups. Sustained low levels of extrinsic pathway inhibitor were observed on postoperative days 1 to 7 in hip surgery patients. Apparently, extrinsic pathway inhibitor is not an acute phase reactant. In uncomplicated surgery, the decreases of the coagulation inhibitor levels are mainly due to hemodilution.
Protein C in citrated plasma is found to be specifically activated by the snake venom derivative Protac, and the activator is used in a simple, automated assay method. The activation is completed in less than 120 s and an isolation of protein C from its inhibitor before activation is not necessary. The activated protein C is determined with the chromogenic substrate S-2366. Therapeutic concentrations of heparin in the test sample do not influence the result. A strong positive correlation to immunoassay of protein C was found (r= 0.92). Three cases of probable hereditary protein C deficiency belonging to the same family were discovered during the study.
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