The first international reference preparation of human parathyroid hormone for immunoassay: characterization and calibration by international collaborative study.

An international collaborative study of an ampouled preparation of highly purified human PTH (hPTH) was carried out on behalf of WHO by 29 laboratories in 12 countries. The results reported here show that the preparation of human PTH, freeze-dried and sealed in ampoules coded 79/500, has appropriate biological activities in in vitro bioassay systems, is free from cleaved products, as shown by high performance liquid chromatography, and is stable under conditions of accelerated thermal degradation. The ampouled hPTH was calibrated by immunoassays against the Research Standard of hPTH for immunoassay (ampoule code 75/549) distributed internationally from the National Institute for Biological Standards and Control since 1977. On the basis of this study and the agreement of the participants, the preparation coded 79/500 was established in 1981 by WHO as the First International Reference Preparation of PTH, Human, for Immunoassay; the unitage was defined as 0.1 IU (100 mIU)/ampoule. An ampouled preparation of unpurified extracted hPTH had characteristics similar to those of the purified ampouled preparation and was calibrated simultaneously to serve as a research reagent for immunoassay. Two ampouled lyophilized materials derived from tissue culture medium and secondary hyperparathyroid plasma, representative of biological fluids widely used as working standards for clinical immunoassays, were included in the collaborative study for comparative purposes. Results from immunoassay, bioassay, and high performance liquid chromatography systems suggest that these preparations contained little intact hPTH and consisted of mixtures of metabolites having predominantly carboxyl region immunoreactivity.