What Is the Specificity of Calcitonin Determination?
The use of a two-site immunoradiometric calcitonin assay improves its specificity by detecting only the monomeric form of circulating calcitonin (20, 21). However, the presence of heterophilic antibodies may still cause falsely elevated values (22, 23). Elevated calcitonin levels unrelated to thyroid diseases are unusual, but can be seen with impaired renal function, pseudohyperparathyroidism, or proton pump inhibitor therapy. Calcitonin-producing tumors other than MTC, particularly neuroendocrine tumors, should also be considered in the differential diagnosis (1). In fact, only 10 to 40% of patients with elevated basal calcitonin levels are ultimately diagnosed with MTC. In patients with benign cytology of their dominant nodule who were, nonetheless, submitted to surgery based on their calcitonin level, only C cell hyperplasia or microscopic MTC was found in some patients, and no C cell abnormalities whatsoever in others (5, 9, 11, 12). Can Diagnostic Performances of Calcitonin Determ
