BACKGROUND/AIM: Medullary thyroid carcinoma (MTC) originates from thyroid C-cells and is a calcitonin-secreting tumor. Calcitonin is also elevated in C-cell hyperplasia (CCH). The objective of the study was to determine the optimal basal (bCT) and peak stimulated calcitonin (psCT) cut-off value for differentiating MTC from CCH, and to examine the histological findings of thyroidectomy in patients with maximum psCT >100 pg/ml. PATIENTS AND METHODS: Fifty-five patients had a maximum calcium-psCT >100 pg/ml and underwent total thyroidectomy. RESULTS: A total of 20 patients were diagnosed with MTC and the remaining 35 with CCH. A bCT level >17.4 pg/ml and psCT level >452 pg/ml demonstrated the best sensitivity and positive predictive value for differenting MTC from CCH. CONCLUSION: The overlap of calcitonin levels between MTC and CCH reduces the accuracy of the calcium stimulation test. Remarkably, an appreciable number of patients with psCT levels >100 pg/ml harbor differentiated thyroid carcinoma of follicular origin.
