Serum calcitonin in thyroid disorders and in pheochromocytoma kindred.

Serum calcitonin was determined by RIA in 59 healthy subjects (Group 1), 49 randomly selected patients with treated or untreated thyroid disorders (Group 2), and in 12 kindred of a pheochromocytoma index case (Group 3). Although most subjects in Group 2 had normal calcitonin levels, there were significant (p less than 0.001) differences between all three groups. Of the five patients in Group 2 with high serum calcitonin, one had medullary cancer of the thyroid, one had multiple endocrine neoplasia, one had acromegaly, and two remained undiagnosed. Increased serum calcitonin levels were also found in seven of 12 normotensive relatives of a patient with pheochromocytoma. It is therefore concluded that high serum calcitonin levels in patients with thyroid disorders strongly suggest the presence of C-cell neoplasia or medullary cancer of the thyroid.