An International Collaborative Study of Factor VIII

Abstract

A collaborative assay was organised to assess the suitability of a replacement for the first International Standard for Factor VIII. Coded samples of a freeze-dried concentrate (proposed 2nd I. S.), the 1st I.S., and a freeze-dried plasma were assayed by 15 laboratories against fresh normal plasma and local standards. Ten laboratories performed 1-stage assays and five 2-stage.The proposed 2nd I. S. had a mean potency of 1.14 International Units per ampoule by direct assay against the 1st I. S.., with no significant difference between one- and two-stage assays. When assayed against a large number of individual normal plasmas, the proposed standard was equivalent to 1.05 ml “average normal plasma” per ampoule. In assays of the common freeze-dried plasma against the 1st I. S., there was a significant difference between assay methods, the 1-stage assays giving higher results for the plasma than the 2-stage. This difference between assay methods confirms results from other collaborative studies, and it seems likely that the 2-stage method is detecting relatively more activity in the concentrate standards.It was agreed by the participants that the proposed material is suitable, in terms of stability and comparability with other materials, to serve as the 2nd International Standard for Factor VIII. The standard was established by WHO at the 28th meeting of the Expert Committee on Biological Standards, with a potency of 1.1 IU per ampoule.