Heparin cofactor II activity in plasma: application of an automated assay method to the study of a normal adult population

A manual chromogenic substrate method for the determination of heparin cofactor II (HC II) activity in plasma has been adapted to the Cobas Bio centrifugal analyzer. By reducing the dermatan sulfate concentration used, interference by opacity was avoided, and the correlation between the manual and the new automated method was high (r = 0.96). Plasma samples from 182 females and 197 males were examined. The mean values of HC II activities in this normal population was relatively high, with a total range of 43-150% and a standard deviation of 17%. 4 apparently healthy individuals had levels below 60%. In males, the mean HC II activity was higher in the 50-59 yr age group than in either the 20-29 yr group or in the group above 60 yr (p less than 0.05). In females, the postmenopausal age group had higher mean HC II activities, but the difference was not statistically significant.

Assay of dermatan sulfate cofactor (heparin cofactor II) activity in human plasma

An assay measuring the thrombin inactivating effect of human plasma in the presence of dermatan sulfate (DS) is described. Test plasma, diluted 1/50, is incubated with human thrombin in the presence of DS. Remaining thrombin is determined with chromogenic substrate 2AcOH . H-D-CHG-Ala-Arg-pNA. Three dilutions of reference plasma suffice and the standard curve is linear. Antithrombin III (AT) exerts a small (3-8%) effect in the assay. When test plasma contains heparin above 0.05 U/ml, this unspecific effect of AT increases, but it may be abolished by antibodies against AT. In a normal material (n = 50), the SD of DS cofactor activity was greater (15%) than that of AT (8.7%). DS cofactor was normal in hereditary AT deficiency and in 15 patients with deep venous thrombosis. In liver cirrhosis and in DIC, both inhibitors were markedly depressed, to similar degrees (r = 0.84).

Inhibition of activated coagulation factor VII by normal human plasma

An amidolytic assay system with tissue thromboplastin (Tpl), purified coagulation factors VII and X, and the chromogenic substrate S-2222 was developed. Antithrombin III (AT) accounts for about one third of the total inhibition exerted by normal plasma in this test system. This effect of AT was prevented by adding purified AT blocking antibodies. Normal plasma and serum showed approximately similar inhibitory effects. The inhibition was probably directed against activated factor VII (F VIIa). Gel filtration of adsorbed normal plasma on Ultrogel AcA 34 showed three inhibitory peaks which were different from AT.