Basal levels of calcitonin were abnormally elevated in 26 of 33 patients with medullary carcinoma of the thyroid. In three patients with nondiagnostic basal concentrations, calcitonin increased to diagnostic levels after calcium infusion; only a ten-minute infusion was needed in one patient. In some patients, the ratio of calcitonin in veins draining the tumor to that in peripheral veins ranged from 4.3 to 57.0. These studies demonstrate the value of the calcitonin immunoassay in the diagnosis and localization of medullary thyroid carcinoma.
Deftos LJ. Radioimmunoassay for Calcitonin in Medullary Thyroid Carcinoma. JAMA. 1974;227(4):403–406. doi:10.1001/jama.1974.03230170019004