Calcitonin is a hormone produced by the C cells of the thyroid gland. Its main role is to help regulate calcium levels in the blood by preventing calcium reabsorption from the bones, reducing calcium absorption in the intestines, and increasing calcium excretion through the kidneys.
High or low calcitonin levels can occur due to thyroid cancer, chronic kidney disease, thyroid removal surgery, or hypothyroidism.
An endocrinologist may order a calcitonin test when thyroid disease is suspected, especially in cases where there is a concern for thyroid cancer. Calcitonin is considered a tumor marker because its levels can rise significantly in certain types of thyroid cancer.
Main function
The main function of calcitonin in the body is to lower calcium levels in the blood by acting in the following ways:
1. Inhibiting osteoclast activity
Osteoclasts are bone cells responsible for breaking down bone tissue and releasing calcium into the bloodstream. By inhibiting osteoclast activity, calcitonin helps prevent excessive calcium release and balance levels of calcium in the blood. This also helps support bone health and prevent osteoporosis.
2. Reducing calcium reabsorption in the kidneys
Calcitonin decreases calcium reabsorption in the kidneys, promoting its elimination through the urine. This helps regulate the concentration of calcium in the blood.
3. Decreasing calcium absorption in the intestines
Calcitonin also reduces calcium absorption in the intestines, further contributing to lower calcium levels in the blood.
Indications for testing
A calcitonin test may be requested by an endocrinologist or primary care provider to:
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Screen for thyroid cancer, particularly when there is a family history of the disease;
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Investigate suspected medullary thyroid carcinoma, a rare type of thyroid cancer;
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Monitor calcitonin levels after thyroid removal surgery;
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Evaluate the effectiveness of thyroid cancer treatment.
In addition, a doctor may order a calcitonin test to monitor the progression of thyroid nodules.
How the test is performed
The calcitonin test is performed in a lab using a blood sample.
1. Basal calcitonin test
The basal calcitonin test measures calcitonin levels in the morning. Fasting for at least 4 hours before the test is usually recommended.
2. Provocative calcitonin test
The provocative calcitonin test helps make results more accurate. It involves the intravenous (IV) infusion of calcium, which stimulates calcitonin production and is typically performed in the morning while fasting. Calcium is injected into a vein, and blood samples are collected at 0, 2, 5, and 10 minutes after the infusion to determine whether the calcitonin response is within the normal range.
Reference values
Calcitonin levels can be affected by factors such as corticosteroid or omeprazole use, age, pregnancy, smoking, and alcohol consumption. For this reason, results should always be interpreted by an endocrinologist alongside other thyroid tests. Reference values may also vary depending on the lab performing the test.
High calcitonin
The main causes of high calcitonin levels include:
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Medullary thyroid carcinoma;
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Excessive growth of thyroid C cells (C-cell hyperplasia);
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Chronic kidney disease;
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Zollinger-Ellison syndrome;
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Hypergastrinemia;
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Frequent or heavy alcohol use.
Other possible causes include leukemia, lung, pancreatic, breast, or prostate cancer, bacterial infection, and hypercalcemia caused by hyperparathyroidism.
Low calcitonin
The main causes of low calcitonin levels are hypothyroidism and thyroid removal surgery. In some cases, genetic factors such as congenital calcitonin deficiency can also lead to low calcitonin levels.