Calcitonin

Definition

Calcitonin, also known as thyrocalcitonin, is a polypeptide hormone secreted by parafollicular C cells of thyroid. It acts directly on osteoclasts to decrease bone-resorbing activity and to cause decreased serum calcium.
Normal range:
- Older children and adults: <12 pg/mL in males; <5 pg/mL in females
- Infants and young children: <40 pg/mL in children <6 months; <15 pg/mL in children 6 months to 3 years (Basuyau)

Serum calcitonin is determined to diagnose recurrence of medullary carcinoma or metastases after the primary tumor has been removed or to confirm complete removal of the tumor if basal calcitonin has been previously increased.
Measurement of serum calcitonin has not been a part of the routine evaluation of patients with thyroid nodules in the United States. The high frequency of falsely high serum calcitonin values and the accuracy of fine needle aspiration biopsy argue against a change in this recommendation. Furthermore, occasional patients with locoregional metastases or locally invasive medullary thyroid carcinoma (MTC) have normal unstimulated serum calcitonin concentrations.

Carcinoma of the lung, breast, islet cell, or ovary and carcinoid due to ectopic production and in myeloproliferative disorders
Hypercalcemia of any etiology, stimulating calcitonin production
Zollinger-Ellison syndrome
C-cell hyperplasia
Pernicious anemia
Acute or chronic thyroiditis
Chronic renal failure

Following surgical therapy for MTC
- In cases of complete cures, serum calcitonin levels fall into the undetectable range over a variable period of several weeks.
- A rise in previously undetectable or very low postoperative serum calcitonin levels is highly suggestive of disease recurrence or spread and should trigger further diagnostic evaluations.

Basal fasting level may be increased in patients with MTC, even when there is no palpable mass in the thyroid.
- Values follow a circadian pattern, with a peak after lunchtime.
- Basal level is normal in approximately one third of cases of MTC.
Levels of >2,000 pg/mL are almost always associated with MTC, with rare cases due to obvious renal failure or ectopic production of calcitonin.
Levels of 500 " 2,000 pg/mL generally indicate medullary carcinoma, renal failure, or ectopic production of calcitonin.
Levels of 100 " 500 pg/mL should be interpreted cautiously with repeat assays and provocative tests. If repeat tests in 1 " 2 months are still abnormal, some authors recommend total thyroidectomy.
This test is not useful for evaluating calcium metabolic diseases.
Falsely elevated values may occur in serum from patients who have developed human antimouse antibodies or heterophilic antibodies.