Defibrination during warfarin therapy in a man with protein C deficiency.

A 57 year old man presented with apparently spontaneous lower extremity deep vein thrombosis and pulmonary embolism. He was treated in conventional fashion with intravenous heparin and oral warfarin. After 4 daily doses of warfarin the prothrombin and proconvertin (P+P) time was within therapeutic range, and heparin was stopped. Over the next six hours complete defibrination occurred, associated with severe bleeding complications. Functional protein C measured after normalization of routine coagulation tests averaged 40% of normal, and was only 3.5% of normal immediately prior to the episode of defibrination. We conclude that the very low functional protein C levels seen immediately prior to defibrination were caused by a combination of pre-existent protein C deficiency and warfarin therapy, and directly predisposed to defibrination once heparin was stopped, despite "therapeutic" warfarin anticoagulation. Exacerbation of intravascular coagulation should be considered a potential prothrombotic effect of warfarin therapy in protein C deficient individuals.