Summary
Twenty-four laboratories participated in a collaborative study to calibrate a replacement
for the 4th International Standard for Unfractionated Heparin (82/502). Both candidate
materials A and B, gave excellent intra- and inter-laboratory variations (majority
of mean %gcv <10%) when assayed against the 4th International Standard. No major differences
of potency estimates were found between methods, although the USP method generally
gave lower potencies than the other methods and candidate B gave a greater variation
between methods than A. Overall, this study showed that the differences between the
candidates are marginal. Based on its narrower molecular weight profile, higher specific
activity and slightly lower inter-method variation, candidate 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 assigned potency of 2031 IU/ampoule.
Key words
Unfractionated heparin - International Standard
