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The Test Sample
What is being tested?
Calcitonin is a hormone produced by special cells in the thyroid called C-cells. The thyroid is a small butterfly-shaped gland that lies over and flat against the windpipe in the throat. It produces calcitonin and several hormones that help control the rate of metabolism, primarily thyroxine (T4) and triiodothyronine (T3). This test measures the amount of calcitonin in the blood.
Calcitonin is involved in the regulation of calcium levels in the blood through inhibiting bone breakdown (resorption) and decreasing kidney reabsorption of calcium. However, its role in calcium regulation is minor compared with parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D. Thus, the measurement of calcitonin in blood is not useful for diagnosis of disorders of calcium regulation.
In two rare conditions, C-cell hyperplasia and medullary thyroid cancer, excessive amounts of calcitonin are produced. C-cell hyperplasia is a benign condition that may or may not progress to become medullary thyroid cancer. Medullary thyroid cancer is malignant – it can spread beyond the thyroid and can be difficult to treat if it is not discovered early.
Medullary cancer is a rare form of thyroid cancer that accounts for 1-2% of all thyroid cancers in the United States. About 75-80% of medullary thyroid cancer cases are sporadic, occurring in those who do not have a family history of the disease. About 20-25% of cases are related to an inherited mutation in the RET gene that leads to multiple endocrine neoplasia type 2 (MEN 2). MEN 2 is a syndrome associated with several related diseases, including medullary thyroid cancer and pheochromocytomas. The altered RET gene is inherited in an autosomal dominant fashion. Only one copy of the mutated gene – from either a father or mother – is required to have a greatly increased risk of developing medullary thyroid cancer. Most cases of sporadic medullary thyroid cancer develop when people are in their 40s or 50s, and the prevalence is higher in women. The inherited form affects both sexes equally and can occur at an earlier age.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
Overnight fasting may be required. Follow the instructions provided by your healthcare practitioner or the laboratory.