[The differential diagnosis of hypercalcitoninism]

Plasma levels of calcitonin (CT) are highest in patients with medullary thyroid carcinoma (MTC). Plasma CT is also raised in some patients with carcinoma such as that of the breast, the lung or the pancreas, and in pheochromocytoma. It must be kept in mind, however, that plasma CT can be similarly raised in patients with renal failure, non-tumoral pulmonary disease or acute pancreatitis. In hypercalcemia patients with primary hyperparathyroidism the plasma CT is normal or only marginally elevated. It is speculated that the raised levels in pregnant and lactating women and in new-born infants prevent excessive bone destruction at times of greater physiological need for calcium. Larger molecular weight forms than monomeric CT (1--32) are circulating at least in plasma of patients with calcitonin-producing tumors and in renal insufficiency. The biological function of these larger molecular weight forms is not yet known. The discrepancies among the results of different laboratories can in part be explained by the immunoheterogeneity of the hormone and the different antigenic recognition sites of the antisera used. The measurement of plasma CT levels is nevertheless important for the diagnosis of MTC and may prove useful in some patients with malignant tumors unrelated to the C-cells of the thyroid gland. CT-radioimmunoassay may be improved by using antibodies specific to the different forms of circulating calcitonin.