A collaborative study to establish the 5th International Standard for Unfractionated Heparin

Twenty-four laboratories participated in a collaborative study to calibrate a replacement for the 4th International Standard for Unfractionated Hepari n (82/502). Both candidate materials A and B, gave excellent intra- and int er-laboratory variations (majority of mean %gcv <10%) when assayed against the 4th International Standard. No major differences of potency estimates w ere found between methods, although the USP method generally gave lower pot encies than the other methods and candidate B gave a greater variation betw een methods than A. Overall, this study showed that the differences between the candidates are marginal. Based on its narrower molecular weight profil e, higher specific activity and slightly lower inter-method variation, cand idate A, 97/578, was proposed and accepted in October, 1998, by the Expert Committee on Biological Standardisation of the World Health Organisation to be the 5th International Standard for Unfractionated Heparin with an assig ned potency of 2031 IU/ampoule.