Multicentre collaborative study to calibrate IGF-II by bioassay and immunoassay: establishment of the First WHO Reference Reagent

A preparation of recombinant insulin-like growth factor-II (IGF-II) (NIBSC code 96/538) was compared with local standards in bioassays and immunoassays by eight laboratories in four countries to assess its suitability for use as a World Health Organisation (WHO) reference reagent. Estimates of relative potencies for the bioassays gave a geometric mean of 1.04 (0.94–1.16) μg of local standard per μg of 96/538. Estimates of relative immunological activities by immunoassay gave a geometric mean of 1.15 (0.94–1.38) μg of local standard per μg of 96/538. The study provided evidence that a common standard for rhIGF-II would be helpful and that 96/538 was sufficiently stable to serve as a reference reagent. Accordingly 96/538 was established as the First WHO Reference Reagent for IGF-II, human, recombinant, and assigned a unitage of 5000 units per ampoule and on the basis of the immunoassay results a nominal mass content of 5 μg per ampoule.