Laboratory determination of heparin cofactor II.

Heparin cofactor II (HC II) is a recently characterized protein that is capable of neutralizing thrombin but not activated factor X. Recent evidence suggests that it may be a physiologically important regulator of thrombin activity. We evaluated and modified a method for clinical laboratory determination of this protein and then utilized the method to analyze HC II activity in various clinical samples. Low levels were associated with liver disease, consumptive coagulopathy, and preeclampsia; normal levels were seen with uncomplicated pregnancy, oral anticoagulant therapy, hereditary antithrombin III (AT III) deficiency, and in 31 patients evaluated for a thrombotic tendency. Except in hereditary AT III deficiency, decreased HC II activity was associated with decreased AT III activity. The potential clinical role of this assay is discussed.