Development and validation of a new radioimmunoassay for parathyrin (PTH).

A radioimmunoassay for human parathyrin has been developed and characterized with whole-molecule (residues 1-84) human parathyrin and with the 1-34, 44-68, and 53-84 amino acid residue fragments of it. The antiserum used reacted with the whole molecule and with the 44-68 and 53-84 fragments, but not with the 1-34 fragment. Parathyrin concentrations in the serum of 118 normal subjects and of 112 patients with surgically proved primary hyperparathyroidism were determined with this assay. The mean results were 39 (SD 13) microL-Eq/mL for the normals and 111 (SD 77) microL-Eq/mL for the patients with primary hyperparathyroidism (p less than 0.0005). The upper 95% confidence limit of the normal range was 60 microL-Eq/mL. For 54 patients with primary hyperparathyroidism, the preoperative values for serum parathyrin, calcium, and phosphate--but not creatinine--were statistically different from the postoperative values (paired t-test, p less than 0.0005). Normal subjects showed significant (p less than 0.0005) differences in serum calcium concentrations but not in parathyrin concentrations, compared with concentrations found in cancer patients and patients who had thiazide-induced hypercalcemia. Phosphate concentration in serum, although not a specific indicator of disease, is a valuable clue to the diagnosis of primary hyperparathyroidism.