DEVELOPMENT OF IN VITRO ASSAY PROCEDURE : EXPERIENCE IN RADIOIMMUNOASSAY FOR PARATHYROID HORMONE

The radioimmunoassay (RIA) for parathyroid hormone (PTH) was reported at first by Berson & Yalow ; 1963. Since then their method of PTH assay have been modified by many authers and new methods have developed. PTH is polypeptide hormone composed of 84 amino acids and has a molecular weight of approximately 9,500. Cleavage of the native PTH yields two principal smaller peptides ; the amino (N) terminal fragment which consists of 34 residues and has its biological activity and the carboxyl (C) terminal which is composed of 50 amino acids residues. We have studied RIA of PTH for these 6 years, which contained following measurements ; c-terminal portion (c-PTH), n-terminal portion (n-PTH) and middle region fragment (MM). The results were as follows : 1) In RD24 RIA system, reproducibility was poor. 2) In EIKEN kit (old one), the recovery was poor. 3) In CIS kit, normal range (1 to 4 mIU/ml) was higher than those of the other c-terminal PTH kits. 4) In RIA-mat (65-84), there is possibility that obtained values included PTH and non functioning PTH like substance. 5) EIKEN (46-84) kit was supposed to be best for the measurement of c-PTH. 6) In n-PTH RIA, obtained values could not differentiate between healthy from various diseases. 7) In PTH-MM (44-68), obtained values seemed to be equal to or slightly higher than those of c-PTH. Measurement of the levels of the c-PTH (or MM) by radioimmunoassay in conjunction with serum calcium determination has become a definitive diagnostic test of parathyroid overactivity.