A sensitive radioimmunoassay of parathyroid hormone in human serum using a specific extraction procedure.

A radioimmunoassay of human parathroid hormone (PTH) is described. PTH was extracted from serum by adsorption to and elution from microfine silica, causing a 3.2-fold greater hormone concentration in extract than in serum. The extraction procedure eliminated from the assay unspecific interference caused by serum factors. The detection limit was 10 pg bovine PTH. The concentration of PTH was measurable in serum from 95% of normal subjects (mean, 68 pg/ml; SD., 18), was undetectable in sera from hypoparathyroid patients, and elevated in 96% of sera from patients with primary hyperparathyroidism. The presented data suggest that the assay mainly measures PTH(1-84).