THE BEHAVIOR OF DIFFERENT FACTOR-VIII CONCENTRATES IN A CHROMOGENIC FACTOR X-ACTIVATING SYSTEM

A chromogenic factor Xa generation method has been developed for compa ring the co-factor activity of factor VIII concentrates at physiologic al factor VIII concentrations (1 iu/ml). In the presence of thrombin a ll concentrates gave similar rapid rates of factor Xa generation, but in the absence of thrombin there were major differences between the ra tes of Xa generation between different products. High purity products, particularly those prepared by monoclonal antibody purification from plasma and recombinant sources, gave more rapid Xa generation than mos t intermediate-purity products. There was a very strong correlation be tween the rate of Xa generation and the difference in factor VIII pote ncy by one-stage and two-stage assays. These results suggest the possi ble presence of small amounts of activated factor VIII in some concent rates, but differences in von Willebrand factor content could also con tribute towards the different rates of factor Xa generation observed.