Improvement of the calcitonin radioimmunoassay.

A rapid and specific assay for human serum calcitonin is described. The total assay-time is under 24 h and uses double-antibody in combination with polyethylene glycol to separate bound and free hormone. The antibody has been checked for its affinity to human serum calcitonin by using a Scatchard plot. Geometric dilution of sera from patients with medullary thyroid carcinoma showed a linear relationship with measured values approximating those expected. The use of Florisil to extract human serum calcitonin from sera to make "human calcitonin-free"-serum for standards has been investigated. A series of 52 normal volunteers and 99 patients with medullary thyroid carcinoma or other possible calcitonin-metabolism disorders have been examined. Only the medullary thyroid carcinoma-patients showed significantly elevated results. In the other groups two patients with phaeochromocytoma and one patient from 29 with bronchial carcinoma had elevated serum calcitonin levels.