Heparin cofactor II (HCII) is a glycoprotein in human plasma which inactivates thrombin rapidly in the presence of heparin or dermatan sulfate. We have developed a functional assay for HCII in which inhibition of thrombin by plasma is determined in the presence of dermatan sulfate. The assay is specific for HCII by the following criteria: (a) under the conditions of the assay, 125I-thrombin forms complexes in plasma which comigrate with the thrombin-HCII complex during sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS- PAGE); (b) activity detected by the assay is decreased in plasma absorbed with monospecific antibodies against HCII; and (c) purified antithrombin III (ATIII) is unreactive in the assay system. Addition of Polybrene to the assay permits determination of HCII activity in samples containing less than or equal to 12 U/mL of heparin. The range of HCII concentrations in normal individuals is 1.2 +/- 0.4 mumol/L (mean +/- 2 SD, n = 34). HCII activity was determined in 54 consecutive patients undergoing evaluation for the possibility of disseminated intravascular coagulation (DIC). Ten of the 11 patients with documented DIC had decreased HCII activity as compared with only 7 of the 43 patients without DIC (chi 2 = 19.3, P less than .0001). The concentrations of HCII and ATIII varied in parallel in most of the patients tested. A significant correlation between decreased HCII activity and decreased serum albumin concentration was also observed in these patients and in eight additional patients with hepatic failure in the absence of DIC. We conclude that HCII activity is decreased in many patients with DIC and hepatic failure.

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