Calcitonin (Thyrocalcitonin)

Calcitonin is a hormone made by special cells in the thyroid gland that helps regulate calcium levels in the body. In clinical practice, it is most importantly used as a marker to detect and monitor a specific type of thyroid cancer called medullary thyroid carcinoma. If your calcitonin level is elevated, your doctor will likely recommend additional tests such as imaging and genetic testing to determine the cause. A low or undetectable level after thyroid surgery for this cancer is a positive sign indicating successful treatment. Mildly elevated levels can sometimes occur for reasons other than cancer, so results are always interpreted alongside other clinical information.

When elevated: Markedly elevated calcitonin levels are strongly associated with medullary thyroid carcinoma and warrant urgent further evaluation including neck ultrasound, genetic testing for RET proto-oncogene mutations, and surgical consultation. Moderately elevated levels may indicate C-cell hyperplasia, a precursor lesion to MTC, or non-thyroidal causes. Very high levels often correlate with metastatic or advanced MTC. When low: Low or undetectable calcitonin levels are generally not clinically significant in isolation and do not indicate a pathological state. After curative surgical resection of MTC, undetectable calcitonin levels are the goal and indicate biochemical remission. Low levels have no established association with adverse outcomes in the general population.

Calcitonin is not a routine marker for athletic performance or training monitoring. It may warrant checking if there is clinical suspicion for medullary thyroid carcinoma (rare), or in the context of bone health assessment in endurance athletes; however, PTH and vitamin D are more standard for evaluating bone metabolism in active individuals.