Standardization of Factor VIII. II. A British Standard for Factor VIII related antigen

A collaborative study on factor VIII related antigen (VIII R:Ag) has been carried out, involving 11 laboratories in the U.K. Samples of two different freeze-dried plasmas were assayed against participants' own local standards by the Laurell electroimmunoassay method. There was reasonably good agreement on the relative potencies of the two freeze-dried plasmas, but there were considerable differences in the VIII R:Ag content of the plasma pools used as local standards, with values ranging from 83% to 129% of the mean. All participants agreed on the need for a standard for VIII R:Ag, and that the unit be defined by the mean of the local standards. Accordingly, freeze-dried plasma 66/355 was established as the 1st British Standard for factor VIII related antigen, with an assigned potency of 1.05 units per ampoule.