Clinical Appraisal of the Radioimrmmoassay of Parathyroid Hormone

Parathyroid Hormone (PTH) in serum was measured by radioimmunoassay using guinea pig antibody to bovine PTH GP-1 and GP-M with either 125I labeled highly purified bovine PTH (bPTH 1-84) or synthetic N-terminal of bovine PTH (bPTH 1-34) in 52 cases of primary hyperparathyroidism, 10 cases of secondary hyperparathyroidism, 20 cases of idiopathic hypoparathyroidism and 10 cases of pseudohypoparathyroidism. While serum PTH was elevated in most patients with primary hyperparathyroidism and undetectable in most patients with idiopathic hypoparathyroidism, normal levels in the former and definitely high values in the latter were occasionally encountered. Combined use of serum Ca, P and Cl measurement and determination of tubular reabsorption of phosphate improved the diagnostic accuracy. Sera of patients with primary hyperparathyroidism always showed a higher N/C ratio or the ratio of immunoreactive PTH measurable by N-terminal active antibody (GP-M) and labeled bPTH (1-34) and that measurable by C-terminal active antibody (GP-100) and labeled bPTH (1-84) than those of patients with secondary hyperparathyroidism with chronic renal failure. While no defference was found in serum Ca, serum alkaline phosphatase and phosphaturic response to exogenous parathyroid hormone among patients with idiopathic hypoparathyroidism with detectable, normal or elevated serum PTH, serum P was slightly lower in the group with elevated serum PTH than in others.