Methodology and clinical significance of heparin cofactor II. Probable heparin cofactor II deficiency in a patient with cerebrovascular thrombosis.

HC II was functionally determined by thrombin inhibition in the presence of heparin in AT III-free plasma prepared by immunoadsorption on anti-AT III-Sepharose 4B column. HC II antigen concentration was assayed using specific antibodies to HC II. Simultaneously, AT III was measured. Plasma levels of HC II and AT III were determined in 110 patients with thrombotic tendency and two patients with obstetric complications and DIC. Highly significant correlations between activity and antigen prove the suitability of the methods. Reduced levels of HC II to about 50% with normal AT III values were repeatedly found in one patient with thrombotic tendency. The course of AT III and HC II during the process of DIC suggests that HC II may function as a thrombin inhibitor reserve when AT III becomes subnormally low.