Heparin cofactor II: an acute phase reactant in patients with deep vein thrombosis.

In human plasma, heparin cofactor II (HCII) is a thrombin inhibitor which displays similarities with antithrombin III (ATIII). As previously reported for hereditary ATIII deficiency, cases of recurrent thrombosis were reported in patients with hereditary HCII deficiency. Here, plasma HCII activity was studied in 372 patients with a history of thrombosis, classified according to their anticoagulant therapy. The mean plasma HCII level was significantly higher in patients with acute deep vein thrombosis (DVT) under heparin therapy than in patients with a history of thrombosis, who were studied more than 3 months after the acute event, and were either on, or had been on, oral anticoagulant therapy. HCII and fibrinogen were significantly correlated in all three groups of patients. These results were strengthened by those of a follow-up study in 23 patients with acute DVT. Changes in plasma HCII activity paralleled those of fibrinogen. This suggests that HCII might behave like an acute phase reactant in patients with thrombosis and that the measurement of its plasma level as a risk factor for thrombosis should be performed some time after the acute episode. In conclusion, the prevalence of HCII deficiency in patients with a history of thrombosis might have been underestimated in series which included patients with acute thrombosis.