Calcitonin, a hormone secreted by the C cells (parafollicular) of the thyroid gland, inhibits bone resorption by regulating the number and activity of osteoblasts. Calcitonin is secreted in direct response to high blood calcium levels and helps to prevent abrupt changes in calcium levels and the excessive loss of calcium.

Measurement of calcitonin is used to diagnose familial medullary thyroid carcinoma (MTC) and postoperatively to detect recurrence or metastasis of thyroid carcinoma. This test is done to measure increases in immunoreactive calcitonin after stimulation with calcium or pentagastrin. Early detection of elevated calcitonin leads to diagnosis of tumor or abnormally secreting C cells before cancer spreads. (Doubling of serum levels correlates with recurrence.) Calcitonin levels are also used in the investigation of families (of a patient with MTC) to detect early subclinical cases of MTC that may exist as C-cell hyperplasia or microscopic MTC.

Men: ≤19 pg/mL or ≤19 ng/L

Women: ≤14 pg/mL or ≤14 ng/L

Calcium Infusion (2.4 mg/kg):

• Men: ≤190 pg/mL or ≤190 ng/L

• Women: ≤130 pg/mL or ≤130 ng/L

Pentagastrin Injection (0.5 μg/kg):

• Men: <110 pg/mL or <110 ng/L

• Women: <35 pg/mL or <35 ng/L

Reference values may differ depending on whether serum or plasma was used. Check with your laboratory.

1. Obtain a 5-mL venous blood specimen in a green-topped tube. Fasting is necessary.

2. Heparinize and chill the blood immediately. If testing is not performed immediately, blood should be frozen. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered. Place the specimen in a biohazard bag.

1. Increased levels of calcitonin are associated with the following conditions:

   1. MTC

   2. C-cell hyperplasia

   3. CKD

   4. Pernicious anemia

   5. Zollinger-Ellison syndrome (increased production of gastrin as a result of a tumor in the pancreas)

   6. Cancer of lung (oat cell lung cancer marker), breast, or pancreas (ectopic calcitonin)

   7. Carcinoid syndrome

   8. Alcoholic cirrhosis

   9. Patients with pancreatitis and thyroiditis

   10. Hypercalcemia of any etiology

2. In a small proportion of patients who do have medullary cancer, the fasting level of calcitonin is normal. In these instances, a provocative test using calcium or pentagastrin should be done.

   1. Very high levels (i.e., 5- to 30-fold increase over basal levels) are evidence of MTC but are not diagnostic.

   2. These stimulation tests are not needed if the basal calcitonin test is diagnostically high.

   3. In patients with elevated calcitonin levels who do not have MTC, the response is not as vigorous.

Pretest Patient Care

1. Explain test purpose and procedure.

2. Remind patient that fasting from food overnight is required. Water is permitted.

3. Be aware that if the provocative tests using calcium and pentagastrin are to be done, the patient is to be fasting also.

   1. Inject pentagastrin 0.5 μg/kg IV push. Draw blood samples before the injection to determine baseline value of calcitonin. Draw a blood sample 1.5, 2, and 5 minutes after the injection.

   2. Inject calcium, 2.0 mg/kg, after baseline sample is drawn. Draw a blood sample 5 and 10 minutes after injection.

4. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.