International reference preparation of human chorionic gonadotropin from immunoassay potency estimates in various bioassay and protein binding assay systems and international reference preparations of the alpha subunit and beta subunit of human chorionic gonadotropin for immunoassay
Storring, P.L.; Gaines Das, R.E.; Bangham, D.R.
Journal of Endocrinology 84(2): 295-310
1980
ISSN/ISBN: 0022-0795 Accession: 005732160
The preparation and nature of the International Reference Preparation of Human Chorionic Gonadotropin (HCG) for Immunoassay (IRP), as well as that of a 2nd batch of ampoules (HCG 75/589) prepared identically from the same HCG preparation, are described. A collaborative study of these materials was carried out by 11 laboratories in 8 countries, using different bioassay and immunoassay methods. Using the various in vivo and in vitro bioassays and receptor assays, the mean log potency estimates for each method within each laboratory of the HCG content of ampoules of the IRP, in terms of the Second International Standard of Human Chorionic Gonadotropin for Bioassay (IS), were homogeneous and gave an overall weighted geometric mean (95% confidence limits) of 650 (632-669) IU/ampoule. There was considerable heterogeneity of potency estimates of the IRP in terms of the IS both within and between many of the immunoassay systems (reflecting the impurity of the IS), and hence attempts to calibrate the IRP with immunoassay systems of different specificities were invalid. Immunoassay estimates of the HCG content of preparations of serum and urine, in terms of the IRP, showed considerable heterogeneity between assay systems (although the degree of this heterogeneity was no greater than that observed using the IS as standard), but the ranking order between preparations was consistent. Confirmation was obtained that contamination of the IRP with HCG-.alpha. and HCG-.beta. subunits was insignificant. Accelerated degradation studies of the IRP stored at increased temperatures suggested that its stability under normal storage conditions would be satisfactory. The IRP apparently was suitable to serve as an international reference preparation for immunoassay, and it was assigned a unitage of 650 IU/ampoule on the basis of bioassay calibration. Since the ampoules of HCG (75/589) did not differ significantly from the IRP in any of the assay systems studied, it appeared to be equally suitable as a reference preparation. The International Reference Preparations of the .alpha. and .beta. Subunits of Human Chorionic Gonadotropin for Immunoassay are also described.