International standards for growth hormone

Since 1955, with the establishment by the World Health Organization of the first International Standard (IS) for bovine growth hormone (GH) for bioassay, there have been a number of developments in the standardization of GH. Two GH ISs are in current use: the IS for human GH established in 1982 and the IS for somatropin (recombinant DNA-derived GH) established in 1994. The availability of two such standards does not encourage reproducibility of GH estimates between different laboratories. The author proposes that the international validation and adoption of the IS for somatropin, which has the advantage of an internationally agreed specific activity of 3 IU/mg, as the primary reference standard for all GH immunoassays would finally eliminate this source of variation in GH estimates.