Homologous radioimmunoassay for human carboxyl-terminal parathyroid hormone and its clinical evaluation.

An homologous radioimmunoassay for human carboxyl-terminal parathyroid hormone (PTH) was developed using the antiserum raised against synthetic human PTH (46-84) and its clinical evaluation was attempted. Antisera were produced in guinea pigs by immunization with synthetic human PTH (46-84) conjugated with BSA. One of the antisera was used at a final concentration of 1 : 10,000 in the assay, and synthetic human PTH (53-84) for a standard and 125I-Tyr45 human PTH (46-84) for a tracer were used. A standard curve was obtained at concentrations from 0.001 to 10 ng per tube of human PTH (53-84). The displacement curves for human PTH (51-84), human PTH (46-84), Tyr45 human PTH (46-84) and bovine PTH (1-84) were almost identical with the standard curve made by synthetic human PTH (53-84). This antiserum, however, did not recognize the human PTH (1-34) fragment at all. Using this assay system, circulating immunoreactive PTH was measured in normal subjects and patients with parathyroid disorders. Normal PTH values in serum ranged from 0.47 ng/ml to an undetectable level (undetectable in two out of 32 normal subjects) and serum PTH values in patients with primary or secondary hyperparathyroidism or idiopathic hypoparathyroidism were almost completely discriminated from normal values. These results suggest that this homologous radioimmunoassay is a carboxyl-terminal specific assay for human PTH and can be quite useful in clinical practice.