Immunoassay for human calcitonin. II. Clinical studies

Abstract

A sensitive and specific radioimmunoassay for human calcitonin has ben developed and applied to clinical studies. Under optimal conditions, the assay can be used to detect 50–100 pg of calcitonin per milliliter of human plasma. Patients with medullary thyroid carcinoma had concentrations of plasma calcitonin that could be readily detected by the assay and ranged from 60 to over 100,000 pg per milliliter. In these patients, hypercalcemia induced by calcium infusion resulted in up to a 20-fold increase in calcitonin concentration. Hypocalcemia induced by EDTA infusion suppressed the secretion of calcitonin in each patient tested. Glucagon infusion had a variable effect on calcitonin secretion. Calcitonin could not be detected with confidence in any basal peripheral sample of plasma taken from normal adults or hypercalcemic patients. Calcitonin could not be unequivocally detected in the majority of thyroid venous plasma samples taken from patients with hypercalcemia. These results suggest that the concentration of calcitonin in the peripheral blood of adults is much lower than previously reported. Further studies are required to determine if calcitonin circulates in peripheral blood even after hypercalcemic stimulation in normal human subjects.