What is the role of biochemical testing in the diagnosis of medullary thyroid carcinoma (MTC)?

Updated: May 09, 2018
  • Author: Pramod K Sharma, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

Answer

Because MTC cells produce calcitonin, elevated serum calcitonin levels are diagnostic of MTC. Although routine measurement of serum calcitonin has low yield in managing the solitary thyroid nodule because of the uncommon nature of MTCs, it is useful in the surveillance of patients with a history of MTC and in managing familial forms. Stimulating calcitonin release by using intravenous pentagastrin increases the sensitivity of the test. For pentagastrin-stimulated calcitonin evaluation, a baseline plasma calcitonin level is measured, followed by the intravenous administration of pentagastrin 0.5 mg/kg and serial measurements of calcitonin 1.5 and 5 minutes after injection. Elevated basal or stimulated calcitonin levels above the normal range for the laboratory strongly suggest MTC.

Plasma calcitonin levels are commonly increased before clinical evidence of MTC appears. Although this finding was once the mainstay in diagnosing familial forms of MTC, results of genetic testing have largely supplanted it. Plasma calcitonin testing is now used for the early detection of MTC in patients already known to be at risk for MTC because of their family history and genetic results. This level is most commonly used as a tumor marker to identify residual and metastatic disease after thyroidectomy to treat MTC.


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