Growth hormone: its measurement and the need for assay harmonization

Serum human growth hormone (hGH) assays show a wide range in bias and in cut-off values for provocative tests, which vary from 13-5 to 35-40 mU/L when they have been established. Studies using novel hGH assays show that methods that are absolutely specific for 22-kDa hGH may not identify bioactive hGH peaks and that 20:22-kDa hGH ratios are increased in acromegaly. Greater harmonization of serum hGH methods can be achieved by: changing from IS 80/505 to IS 98/574, which is calibrated in mass units of recombinant 22-kDa hGH; using monoclonal/polyclonal or polyclonal/polyclonal antibody combinations that measure both 20-kDa and 22-kDa hGH; the development of assays such as the immunofunctional hGH assay which has the convenience of an immunometric assay but gives results that correlate better with bioassays; collaboration between manufacturers and laboratories to establish method-related cut-off limits for provocative tests of hGH status.