STUDIES OF CIRCULATING PARATHYROID HORMONE IN MAN USING A HOMOLOGOUS AMINO‐TERMINAL SPECIFIC IMMUNORADIOMETRIC ASSAY

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Abstract
Circulating immunoreactive parathyroid hormone (PTH) was measured by a homologous, amino-terminal, specific, immunoradiometric assay in man. In 42 healthy subjects the concentrations ranged between < 40 pg/ml and 120 pg/ml. No hormone could be detected in the sera of 11 patients with hypoparathyroidism, but the concentrations were clearly elevated in 6 patients with pseudohypoparathyroidism (range 190-1120 pg/ml). In 35 patients with primary hyperparathyroidism the mean (.+-. standard error of the mean) concentration was 283.4 .+-. 42.4 pg/ml (range 100-1350 pg/ml). A significant positive correlation was demonstrated between immunoassayable hormone and serum Ca concentrations in these patients. In 9 patients PTH concentrations were measured before and after parathyroidectomy. In all of them they were elevated pre-operatively but fell to the normal range after parathyroidectomy. The disappearance of exogenously administered synthetic human PTH (1-34) from the circulation of 2 normal subjects was rapid with an apparent plasma half-disappearance time (t1/2) between 2 and 3 min; the metabolic clearance rate was 12.9 and 9.0 ml kg-1 per min, respectively. Similarly, the disappearance of endogenous, amino-terminal, immunoreactive PTH from the circulation of 2 patients with primary hyperparathyroidism after parathyroidectomy was rapid; the apparent t1/2 was .apprx. 3 min. Homologous amino-terminal specific immunoassays for PTH can thus be useful for the study of both the acute, and chronic, changes of circulating hormone in man and represent an improvement over heterologous unselected assay systems.