PLASMA FVIII LEVELS MEASURED AFTER INFUSION OF RECOMBINANT F VIII (rFVIII) VARY SIGNIFICANTLY WITH DIFFERENT ASSAY METHODS - (WILL THE REAL FVIII LEVEL PLEASE STAND UP!). † 934

Abstract

As part of a bioequivalence study comparing two lots of rFVIII(Kogenate®), 9 persons with hemophilia A were infused with rFVIII from each lot, and multiple plasma samples were then obtained from each subject for determination of FVIII assays over 48 hrs. Samples were assayed by 4 different methods: chromogenic, and one stage APTT method using 3 different types of activators (A)-micronized silica, ellagic acid, and kaolin. All samples were immediately centrifuged, snap frozen and stored at -70°C until assayed in duplicate. The same reference plasma standard was used throughout. Results, shown below, indicate a consistent difference in F VIII assay values, with those run by chromogenic substrate method being roughly twice as high as those run by one-stage APTT method with kaolin as A. One stage results with micronized silica or ellagic acid as A were comparable, and were consistently higher than those with kaolin. Most U.S. clinical labs use a one-stage assay, with micronized silica or ellagic acid A. Because significantly different results can be obtained depending on F VIII assay method used, multicenter studies must carefully standardize assay techniques and reagents in order to combine data for analysis. Additionally, such differences have significant cost implications (partially funded by Bayer). Figure