North American Study of Factor VIII Concentrate Potency

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Abstract
In view of reports of less than labelled F VIII:C content in some lots of commercially available f VIII concentrates, a multi‐center prospective study of f VIII concentrate potency was organized in collaboration with the United States Bureau of Biologics (BoB). Phase one of the study was aimed at evaluating the reproducibility of F VIII:C assays (one stage) in the participating laboratories, using: 1) A uniform assay method, and 2) Each lab's in‐house method. Reproducibility was better with the latter. Phase two consisted of: 1),In vitroassays of currently available F VIII concentrates, and 2)In vivoF VIII:C recovery studies in two severe hemophilia A subjects. Three different lots of concentrate from each of eight different products were used for these studies. Lots were randomly selected from those available in spring‐summer 1982.Each lab used its in‐house F VIII:C method, with lyophilized standards provided by BoB. All values were read against three standards: In‐house, BoB A (concentrate standard) and BoB s (plasma standard). Baseline, 15 and 45 minute samples from thein vivorecovery studies were snap‐frozen and stored at ‐70°C, then shipped in dry ice. All plasma samples were assayed as unknowns in each of nine participating labs (the authors‘, Hyland, Cutter and BoB). Statistical analysis of data for 24 lots of concentrate (three lots each from Cutter, Hyland, Alpha, Armour, N.Y. Blood Center, American Red Cross‐Cutter, American Red Cross‐Hyland, Michigan Department of Health) revealed the following: Inter‐lab values of in vitro assays of concentrate compared best when BoB A (concentrate standard) was used. Mean values corresponded to those on the manufacturers' labels, and in some instances were higher. In vivo studies revealed better than “expected” F VIII:C recovery with each product tested. In the in vivo studies inter‐lab values (for f VIII:C assays of the plasma samples) compared very well when BoB 5 (plasma standard) was used. In bothin vitroand in vivo studies there was much greater inter‐laboratory variation in results when in‐house standards were used.