Protein C: an automated activity assay.

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.