Calcitonin

The calcitonin test is primarily used 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 of MTC following treatment. It is also used to screen for MTC in family members of patients with MEN 2. Baseline calcitonin results may be useful if MTC is suspected but, it is not routinely recommended for all thyroid nodules.

Tests which attempt to stimulate the levels of calcitonin are more sensitive than calcitonin measurements alone. These tests involve collecting a sample before stimulation, then giving the patient an injection of intravenous calcium and/or 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. This test is also performed to diagnose MTC pre-operatively in relatives of patients with familial MTC, when there are false-positive baseline calcitonin levels or when the levels are only slightly raised.

Calcitonin may be requested when a patient is suspected of having C-cell hyperplasia or MTC, but not with all thyroid nodules. Stimulation tests may be used 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 requested at regular intervals to monitor treatment effectiveness and recurrence. Immediate postoperative samples are collected no earlier than 10 days after thyroidectomy and it should also be fasting samples if possible. In long term follow up, calcitonin is measured usually 6 months after surgery.

An elevated concentration of calcitonin means that excessive amounts are being produced. Significantly elevated concentrations 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 will usually fall to very low concentrations. If the values stay low over time, then it is likely that the treatment was effective. In some cases, calcitonin will fall but remain moderately elevated after treatment. This means that some calcitonin-producing tissue remains. It will also depend upon baseline calcitonin before the surgery and the stage of the tumour at the presentation. 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.

Other thyroid tests, such as Free T4, Free T3, and TSH, are usually normal when calcitonin concentrations are elevated.

C-cell hyperplasia and MTC are both sufficiently rare that it is not useful to screen for calcitonin in the general population.