Determination of calcitonin levels in C-cell disease: clinical interest and potential pitfalls.

An elevated serum calcitonin level is a highly sensitive marker for medullary thyroid carcinoma (MTC) that can be used for screening, differential diagnosis, prognostic assessment, follow-up monitoring, and assessment of treatment response. Nevertheless, additional data are required to definitively support routine measurement of calcitonin levels in the initial work-up of patients with thyroid nodules, mainly because there is no convincing evidence that such testing actually reduces MTC-related mortality. By contrast, the prognostic value of measuring calcitonin levels preoperatively, postoperatively, and during follow-up of patients with MTC is widely acknowledged. Furthermore, determination of calcitonin levels is also used to evaluate the response of MTC to novel forms of systemic treatment, such as tyrosine kinase inhibitors. In this Review, we discuss the key issues surrounding the use of this laboratory test in the clinical management of patients with MTC.