What is being tested?
This test measures the amount of calcitonin in the blood. The function of calcitonin in the human body is unknown; what is known is that it is a hormone produced by C-cells in the thyroid. The thyroid is a small butterfly-shaped gland that lies over and flat against the windpipe in the throat. It produces several hormones, primarily T4 (thyroxine) and T3 (triiodothyronine), that help control the rate of metabolism.
In two rare conditions, C-cell hyperplasia and medullary thyroid cancer (MTC), excessive amounts of calcitonin are produced. C-cell hyperplasia is a benign condition that may or may not progress to become MTC. MTC is malignant - it can spread beyond the thyroid and can be difficult to treat if it is not discovered early.
About 75-80% of MTC cases are sporadic, but about 20-25% are related to an inherited mutation in the RET gene that leads to multiple endocrine neoplasia type 2 (MEN 2), a syndrome associated with several related diseases, including MTC. The altered RET gene is inherited in an autosomal dominant fashion (only 1 copy of the mutated gene - from either your father or mother - is required to have a greatly increased risk of developing MTC). Most cases of sporadic MTC develop when patients are in their 40s or 50s and the prevalence is higher in women, but inherited MTC affects both sexes equally and can occur at an early age.
How is it used?
The calcitonin test is primarily ordered to help diagnose C-cell hyperplasia and medullary thyroid cancer (MTC), to evaluate the effectiveness of treatment for MTC, and to monitor patients for recurrence. It is also used to screen for MTC in family members of patients with multiple endocrine neoplasia type 2 (MEN 2).
Stimulation tests are more sensitive than calcitonin measurements alone. This involves collecting a baseline sample, then giving the patient an injection of intravenous calcium or less commonly, pentagastrin to stimulate calcitonin production. Several more blood samples are then collected over the next few minutes to gauge the effect of the stimulation. Patients with early C-cell hyperplasia and/or MTC will usually have very significant increases in their levels of calcitonin during this test.
When is it requested?
Calcitonin levels may be ordered when a patient is suspected of having C-cell hyperplasia or medullary thyroid cancer. Stimulation tests may be ordered when a patient has indeterminate or normal calcitonin results but clinical suspicions remain. These tests may be regularly performed on family members of patients who have MEN 2, starting at an early age, in order to detect MTC or C-cell hyperplasia as soon as it occurs. When someone has been treated for MTC, calcitonin testing will usually be ordered at regular intervals to monitor treatment effectiveness and recurrence.
What does the result mean?
An elevated concentration of calcitonin means that excessive amounts are being produced. Significantly elevated levels of calcitonin are a good indicator of C-cell hyperplasia or MTC; however, the doctor will use other procedures, such as a thyroid biopsy, scan, and ultrasound, to confirm the diagnosis.
With successful treatment for MTC (removal of the thyroid gland and often some surrounding tissues), calcitonin levels will usually fall to very low levels. If the values stay low over time, then it is likely that the treatment was effective. In some cases, calcitonin levels will fall but remain moderately elevated after treatment. This means that some calcitonin-producing tissue remains. Doctors will monitor calcitonin and watch for increases over time. If calcitonin levels begin to rise, then it is likely that there is a recurrence of MTC.
Is there anything else I should know?
Genetic (DNA) tests are also used in patients suspected of having MEN2, to check if the person carries the abnormal gene that causes the condition.
Other thyroid tests, such as free T4, free T3, and TSH, are usually normal when calcitonin levels are elevated.
Concentrations of calcitonin may be increased with use of drugs such as epinephrine, glucagon, and oral contraceptives, and are normally higher in newborns as well as in women during pregnancy.
Other conditions with elevated calcitonin include:
C-cell hyperplasia and medullary thyroid cancer are both sufficiently rare that it is not useful to screen for calcitonin in the general population.
No, the body can function without it. But you will need to take other thyroid hormones, usually thyroxine (T4), to regulate your metabolism.
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