Calcitonin

Test Description


Calcitonin, a polypeptide hormone secreted by the C cells of the thyroid, assists in
the regulation of serum calcium and phosphorus levels. When an elevated level of
calcium is present in the blood (hypercalcemia), calcitonin is secreted. This results
in inhibition of calcium absorption from the gastrointestinal tract, inhibition of
calcium resorption from the bone by osteoclasts and osteocytes, and increased
excretion of calcium by the kidneys. These actions are antagonistic to parathyroid
hormone and result in lower serum calcium levels. The test is used primarily to evaluate
suspected medullary carcinoma of the thyroid (MTC), which is characterized
by hypersecretion of calcitonin in the presence of normal serum calcium levels. In
some patients who have medullary cancer of the thyroid, the fasting level of calcitonin
is normal. If this occurs, a provocative testing involving intravenous pentagastrin
or calcium administration is used.
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THE EVIDENCE FOR PRACTICE
Although studies have suggested that, in the evaluation of a thyroid nodule, the routine
measurement of serum calcitonin is a cost-effective and important technique to avoid
missing medullary thyroid cancer, not all clinicians agree that screening calcitonin is
useful.
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Normal Values

Basal:
            Female: <14 pg/mL (<14 ng/L SI units)
            Male: <19 pg/mL (<19 ng/L SI units)

Postcalcium infusion (administered at 2.4 mg/kg):

            Female: <130 pg/mL (<130 ng/L SI units)
            Male: <190 pg/mL (<190 ng/L SI units)

Postpentagastrin injection (administered at 0.5 mcg/kg):

             Female: <35 pg/mL (<35 ng/L SI units)
             Male: <110 pg/mL (<110 ng/L SI units)
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Possible Meanings of Abnormal Values
Increased
Alcoholic cirrhosis
Breast cancer
C-cell hyperplasia
Chronic renal failure
Cushing’s disease
Ectopic calcitonin production (as with pancreatic cancer)
Hypercalcemia
Islet cell tumors
Lung cancer (oat cell)
Medullary thyroid cancer
Parathyroid adenoma
Parathyroid hyperplasia
Pernicious anemia
Pheochromocytoma
Thyroiditis
Uremia
Zollinger-Ellison syndrome
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Contributing Factors to Abnormal Values
• Drugs that may increase calcitonin levels: calcium, epinephrine, glucagon, oral contraceptives,
pentagastrin.
• Hemolysis of the blood sample may alter test results.
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Interventions/Implications

Pretest
• Explain to the patient the purpose of the test and the need for a blood sample to be
  drawn.
• Overnight fasting is preferred. Water is permitted.

Procedure
• A 1-mL serum sample is collected in red-top (no gel) tube and placed on ice.
• 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 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.
• Gloves are worn throughout the procedure.

Posttest

• Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued
  bleeding.
• The sample is labeled and transported to the laboratory.
• Report results to the primary care provider.
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Clinical alert             

•If the patient is found to have medullary thyroid cancer and surgery is performed,
follow-up calcitonin levels are checked periodically to ensure that levels
return to normal. If levels remain elevated, some calcitonin-producing tissue
remains. If levels lower after surgery and later rise, the cancer may have
returned.
• It is suggested that family members of patients with medullary cancer of the thyroid

be screened via the calcitonin test.