Biological standardization of cytokines and growth factors.

To quantify the biological activity of different cytokine preparations with different specific activities by bioassay, mass units cannot be used and biological activity has to be expressed as << biological potency units >>. The biological unit requires definition by a standard that is assay-independent (especially when measuring a particular type of biological activity). Once the unit is defined, it can be used in any laboratory, thus providing a means of ensuring uniformity throughout the world in the designation of potency of different biological preparations. The World Health Organisation (WHO) standardization programme involves the production of biologically stable, well-characterised potency and immunoassay standards that are available world-wide using a single international unitage. These international standards have been used to reduce dramatically the variation in estimates of cytokine preparations within and between laboratories for immunoassays and bioassays.