Relationship between factor XII, von Willebrand factor and postoperative deep vein thrombosis.

The development of postoperative deep vein thrombosis (DVT) was studied in 45 patients subjected to major abdominal surgery, 17 of whom showed signs of DVT as defined by 125I-fibrinogen test. The preoperative levels of von Willebrand factor (F VIII RAg) and platelets were higher in these 17 patients than in those remaining free from DVT. A contributing factor in DVT development thus may be more active primary haemostasis. Preoperative F XII levels were similar in the two groups, but the post-operative drop in F XII was more pronounced in the DVT group. An inhibitor of plasminogen activation behaved similarly in both groups. C1-inhibitor, the main inhibitor of the F XII-dependent clotting and fibrinolytic pathways, showed a typical acute-phase response postoperatively, without intergroup difference. The study suggested that F XII-dependent pathways play a role in the genesis of venous thrombi, at least in the postoperative period, though whether the postoperative F XII drop was due to a role in clotting or to fibrinolysis activation remains unclear.