Calcitonin

What is being measured?
This test measures the amount of calcitonin in the blood. The role of calcitonin in the human body is not known; what is known is that it is a hormone produced by the C cells of the thyroid. The thyroid is a small, butterfly-shaped gland that lies over and against the windpipe in the throat. It produces several hormones, mainly T4 (thyroxine) and T3 (triiodothyronine), which help control metabolism.

In two rare conditions, C-cell hyperplasia and medullary thyroid cancer (MTC), large amounts of calcitonin are produced. C-cell hyperplasia is a benign condition that may or may not progress to MTC. MTC is malignant: it can spread beyond the thyroid and is difficult to cure if not detected early.

About 75-80% of cases of MTC are sporadic, but about 20-25% are due 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 pattern (only one mutated copy of the gene, from either the father or the mother, is needed to have a greatly increased risk of developing MTC). Most sporadic cases of MTC develop when patients are in their 40s or 50s and are more common in women, but inherited MTC affects both sexes equally and can appear at an early age.

How is the sample collected?
A blood sample is obtained by inserting a needle into a vein in the arm

How is it used?
When is it requested?
What does the result mean?
Is there anything else I should know?

How is it used?
The calcitonin test is mainly requested to help diagnose C-cell hyperplasia and medullary thyroid cancer (MTC), to assess the effectiveness of treatment for MTC and to monitor patients for recurrence. It is also used to monitor for MTC in family members of patients with MEN 2.

Stimulation tests are more sensitive than measuring calcitonin alone. A baseline sample is taken, then the patient is given an intravenous injection of calcium or pentagastrin to stimulate calcitonin production. Several blood samples are then taken over the following minutes to assess the effect of the stimulation. Patients with early C-cell hyperplasia and/or MTC usually have significant increases in their calcitonin levels during this test.

When is it requested?
Calcitonin levels may be requested when a patient is suspected of having C-cell hyperplasia or medullary thyroid cancer. A recent study also recommends measuring calcitonin before surgery in all patients with thyroid nodules, but not everyone agrees. Stimulation tests may be requested when a patient has borderline or normal calcitonin results but clinical suspicion remains. These tests may be carried out regularly on family members of patients with MEN 2, starting at an early age, so as to detect MTC or C-cell hyperplasia as early as possible. When someone has been treated for MTC, the calcitonin test is usually requested at regular intervals to monitor the effectiveness of treatment and check for recurrence.

What does the result mean?
A high calcitonin concentration means that large amounts are being produced. Significantly raised calcitonin levels are a good indicator of C-cell hyperplasia or MTC; the doctor may use other procedures, such as a thyroid biopsy or an ultrasound scan, to confirm the diagnosis.

With effective treatment of MTC (removal of the thyroid and often some surrounding tissue), calcitonin levels usually fall to very low levels. If the values stay low for a long time, the treatment has probably been effective. In some cases calcitonin levels fall but remain moderately raised after treatment. This means that some calcitonin-producing tissue remains. The doctor will monitor calcitonin. If calcitonin levels start to rise, MTC has probably come back.

Is there anything else I should know?
Other thyroid tests, such as T4, T3 and TSH, are usually normal when calcitonin levels are raised.

1. Why is the calcitonin test not used for routine screening?
2. If my thyroid is removed, will I need to replace my calcitonin?
3. Is calcitonin ever used as a supplement?

1. Why is the calcitonin test not used for routine screening?
C-cell hyperplasia and MTC are both rare enough that testing calcitonin in the general population is not useful.

2. If my thyroid is removed, will I need to replace my calcitonin?
No, the body can function without it. But you will need to take other thyroid hormones (usually T4) to regulate your metabolism.

3. Is calcitonin ever used as a supplement?
Yes, but in a completely different context. Because it inhibits bone resorption when given in large amounts, calcitonin is sometimes given as a medicine to people with osteoporosis: it helps maintain bone density and has a pain-relieving effect on bone.