Protein C response to induction of warfarin treatment after coronary bypass operation

To investigate the effect of warfarin on the anticoagulant pathway, protein C antigen and activity levels were compared in two groups of patients treated with different regimens of sodium warfarin during the initial stage of anticoagulant therapy following heart surgery. Group I received 6 mg of warfarin per day for 3 days. Group II received 8 mg twice a day for 2 or 3 days. Preoperative levels of Protein C antigen and activity averaged 108 +/- 16% and 102 +/- 18% (mean +/- SD), respectively, and by one hour after the operation, levels had fallen significantly (protein C antigen to 76 +/- 14%; protein C activity to 70 +/- 16%). After the initiation of warfarin treatment, the levels of protein C activity in group II were significantly lower than those of group I. In contrast, the reductions in factor X were much slower and were similar in the two groups. As the factor X level reflects the antithrombotic effect of warfarin, this result suggests that the rapid reduction of protein C activity may have given rise to a transient hypercoagulable state in the patients of group II.