BACKGROUND: Routine measurement of serum calcitonin to detect medullary thyroid carcinoma (MTC) continues to be fiercely debated, although less attention has been paid to the positive predictive value (PPV) of this method. METHODS: We collected data from 959 patients with nontoxic nodular goiter; thyroidectomy was performed in 307 of these patients. RESULTS: Thirty-nine patients had elevated serum calcitonin; 6 of these patients had MTC detected by the initial diagnostic setup. No additional patient in the cohort was registered in the Danish Thyroid Cancer Database, reflecting that all patients with MTC were classified correctly initially. The sensitivity of serum calcitonin for detection of MTC was 100%, the specificity was 95.3%, the positive predictive value was 15.4%, and the negative predictive value was 100%. CONCLUSION: Serum calcitonin has high sensitivity and specificity for detection of MTC. The low PPV might lead to unnecessary thyroid surgery. Thus, the result of serum calcitonin measurement should always be interpreted in the context of other clinical variables.
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