Assay of AHF concentrates and standards: failure to eliminate variability with a monographed assay.

Previous calibration studies have shown a high interlaboratory variability in the potency of the proposed Office of Biologics (National Center for Drugs and Biologics, US-FDA) AHF standard relative to the 2nd International Standard for Factor VIII (Factor VIII:C) (WHO 73/552). This led to the formation of an Industry Collaborative Study group whose objective was to reduce the assay variability. The group, in collaboration with the Office of Biologics and the National Institute for Biological Standards and Control (UK), designed a study based on a monographed one-stage assay protocol, which specified all materials, assay methods, equipment, dilution technique, reagents, assay order, and calculation methodology.