Measurement of intact human parathyrin by an extracting two-site immunoradiometric assay

Abstract

This is an immunoradiometric assay of intact human parathyrin, hPTH(1-84). One antibody, directed against the N-terminal part of the hormone, was produced in goats and conjugated covalently to cellulose particles. hPTH(1-84) and the N-terminal fragments were extracted from EDTA-treated plasma by these particles and thus concentrated. Another antibody, against synthetic hPTH(53-84), was raised in rabbits; this bound to the C-terminal part of the hormone. The final step was labeling the second free binding site of this antibody with 125I-labeled Tyr52-hPTH(53-84) and measuring the bound radioactivity. This assay can detect intact PTH in concentrations as low as 0.6 pmol/L (1.2 X 10(-16) mol per tube). The assay did not cross react with hPTH(1-34), hPTH(1-44), hPTH(28-48), hPTH(39-84), hPTH(44-68), or hPTH(53-84) in concentrations up to 6400 pmol/L. In 60 normal subjects, hPTH(1-84) concentrations ranged from 1.9 to 6.8 pmol/L; in 32 patients with primary hyperparathyroidism, from 7.0 to 80 pmol/L. The hormone was not detected in four patients with hypoparathyroidism.