Human calcitonin radioimmunoassay: characterization and application.

A radioimmunoassay of human calcitonin (HCT) has been developed, employing antibodies formed in response to a HCT-bovine gamma globulin conjugate. The assay is sensitive (lower limits of detection 30 pg/ml serum), reproducible, and specific for intact HCT and carboxyl-terminal fragments of HCT. Serum HCT was detected in 76% of 63 normal subjects (mean +/- S.E.M. = 72 +/- 7 pg/ml), and was increased in cord sera, as well as sera from patients with chronic renal disease and medullary thyroid cancer. Increased levels were observed during calcium infusion into normal subjects, but not in sera from pregnant women or subjects with chronic hypercalcemia. No significant correlation was observed between serum ionized calcium and HCT in sera from 147 hospitalized patients. These findings suggest the usefulness of this assay for further studies of conditions affecting calcitonin homeostasis.