An effect of predilution on potency assays of factor VIII concentrates

The effect of prediluent on potency assays for Factor VIII concentrates was evaluated systematically using a well defined one stage Factor VIII assay. It was demonstrated that potency values were higher when Factor VIII deficient plasma was used as the prediluent compared to identical assays performed when barbital buffered saline solution was used as prediluent. Prediluent is therefore an important variable to evaluate in establishing the validity of any proposed Factor VIII potency assay. Since the goal of Factor VIII potency measurement is to predict therapeutic effect, the use of Factor VIII deficient plasma is the more satisfactory alternative where a difference exists, since this diluent approximates best the conditions which occur when a Factor VIII concentrate is injected into the bloodstream of a patient with hemophilia A.