Variations of plasma calcitonin levels measured by radioimmunoassay systems for human calcitonin.

Radioimmunoassay systems of different characteristics are available for routine determination of human calcitonin (hCT). The purity and calcitonin content of the used standards has to be observed, different antisera may yield discrepant absolute values from the same plasma samples. HCT measurements permit blood level control during treatment with this hormone. In most thyroidectomized patients hCT is not measurable--it is supposed that there is no relevant extrathyroidal calcitonin production in man. HCT RIA systems also recognize rat calcitonin. In this species, chronic hypercalcemia first leads to increased calcitonin secretion which is soon followed by a decrease. Presumably, this fall reflects down-regulation of calcitonin secretion which is more a calcium conserving than an anti-hypercalcemic hormone.