Influence of chronic autoimmune thyroiditis and papillary thyroid cancer on serum calcitonin levels

Serum calcitonin (sCt) is measured in many patients with nodular thyroid disease, and the possibility of a false-positive result is a matter of concern, particularly in the case of mild hypercalcitoninemia. Among the conditions reported to cause sCt elevation, Hashimoto's thyroiditis (HT) and papillary thyroid carcinoma (PTC) are relevant. In view of the high frequency of these conditions in patients with nodular disease and the controversy regarding the extent to which they contribute to hypercalcitoninemia, the objective of this study was to determine the influence of the presence of HT and PTC on sCt levels.

Three groups of patients >12 years of age were studied. The first group (group A, n=492) consisted of patients with nodular disease evaluated before thyroidectomy and without medullary thyroid carcinoma (MTC) upon histology. The second group (group B, n=583) consisted of subjects without nodules on ultrasound. The third group (group C, n=62) consisted of patients with PTC and distant metastases after total thyroidectomy. The levels of sCt and frequency of elevated sCt were compared in patients with versus without HT (groups A and B) and those with PTC>1 cm versus without PTC (group A).

No difference in sCt levels or in the frequency of elevated sCt was observed between patients with and without HT, irrespective of sex. Moreover, the presence of PTC>1 cm did not influence sCt levels or the frequency of hypercalcitoninemia. In fact, none of the 1075 patients in groups A and B had sCt>40 pg/mL, regardless of the presence of HT and PTC. Serum calcitonin was undetectable in any patient of group C.

The finding of hypercalcitoninemia in patients with nodular disease should be interpreted as a suspicion of MTC, even in the presence of associated HT or cytology suggestive of PTC.