Calcitonin is a hormone that is released by the C-cells of the thyroid gland. The secretion of calcitonin is triggered when calcium levels in the blood are elevated. Calcitonin contributes to calcium hemostasis by decreasing calcium levels in the blood through the inhibition of bone resorption and increasing excretion of calcium by the kidneys.
Reasons for Performing Calcitonin Testing
Usually this test is used to evaluate patients suspected of having medullary cancer of the thyroid. Up to 75% of these patients have elevated secretion of calcitonin despite having normal blood calcium levels. This test is also used as a screening aid in persons with a family history of thyroid cancer, as a tool to monitor progress of treatment of thyroid cancer. Having a screening calcitonin level can detect thyroid cancer in the early stages while there is good chance for a cure. Also associated with elevated calcitonin levels is C-cell hyperplasia, a benign disease.
In addition to thyroid cancer, elevated calcitonin levels may also be seen in cancers of the lungs, breast, or pancreas. Sometimes levels are elevated in normal pregnant females and in neonates. Other causes for calcitonin elevation include kidney disease, certain medications, thyroid inflammation, primary hyperparathyroidism, anemia, and liver cirrhosis.
A doctor may decide to order the tests if you are having symptoms of a problem such as a lump or swelling at the front of the neck, throat pain or frontal neck pain, hoarseness or voice changes, difficulties with breathing or swallowing, or unexplained cough. Recent studies also suggested that the test should be performed prior to surgery in all patients with thyroid nodules; however, this is controversial.
An elevated serum calcitonin test should be followed by a provocative test using an IV infusion of pentagastrin or calcium. In these tests, blood is drawn prior to the test to determine baseline calcitonin levels, and then the chosen medication is administered by IV. Blood tests for calcitonin are drawn at specific time intervals. With medullary cancer of the thyroid or C-cell hyperplasia, calcitonin levels will rise dramatically in response to provocative testing. For patients who have a positive provoked calcitonin test result, doctors will usually schedule a thyroid biopsy to be performed.
Normal results for calcitonin levels are variable depending on the lab doing the testing, whether the test is provoked or non-provoked, whether calcium or pentagastrin is used in provoked tests, and whether the patient is male or female. For these reasons, only a physician can determine whether the results of a particular calcitonin test represent an abnormality.
Pagana KD, Pagana TJ (2005). Mosby’s Manual of Diagnostic and Laboratory Tests, 7th ed. St. Louis: Mosby.