Type of test : Blood

Normal findings

Basal (plasma) Males: ≤ 19 pg/mL or ≤ 19 ng/L (SI units) Females: ≤ 14 pg/mL or ≤ 14 ng/L (SI units)

Calcium infusion (2.4 mg/kg) Males: ≤ 190 pg/mL or ≤ 190 ng/L Females: ≤ 130 pg/mL or ≤ 130 ng/L

Pentagastrin injection (0.5 mcg/kg) Males: ≤ 110 pg/mL or ≤ 110 ng/L Females: ≤ 30 pg/mL or ≤ 30 ng/L

Procalcitonin < 2 ng/mL

Test explanation and related physiology

 Calcitonin is a hormone secreted by the parafollicular or C-cells of the thyroid gland. Its secretion is stimulated by elevated serum calcium levels. The purpose of calcitonin is to contribute to calcium homeostasis.

This test is usually used in the evaluation of patients with or suspected to have medullary carcinoma of the thyroid. This is a cancer of the thyroid with a familial tendency; if it is found late, it has a poor prognosis. Routine screening for elevated calcitonin levels can detect medullary cancer early and can improve chances for cure. C-cell hyperplasia, a benign calcitonin-producing disease that also has a familial tendency, is also associated with elevated calcitonin levels.

Equivocal elevations in calcitonin levels should be followed with further provocative testing using pentagastrin or calcium to stimulate calcitonin secretion. Pentagastrin stimulation involves an intravenous (IV) infusion with blood samples drawn before the injection and at 90 seconds, 2 minutes, and 5 minutes after the infusion. The calcium infusion test can be performed in a variety of ways but is most commonly administered with baseline and 5- and 10-minute postinfusion blood levels.

Elevated levels of calcitonin also may be seen in people with cancer of the lung, breast, or pancreas. This is probably a form of paraneoplastic syndrome in which there is an ectopic production of calcitonin by the nonthyroid cancer cells.

Procalcitonin (PCT) is a peptide that shares a common structure with the prohormone of calcitonin. During episodes of severe bacterial infection, sepsis, or trauma, the amount of blood-circulating PCT increases. PCT can, therefore, aid in the risk assessment of critically ill patients. The levels are sometimes trended to assess for progression to severe sepsis or for improvement of infection.

 Interfering factors

• Levels are often elevated in pregnancy and in newborns.

*Drugs that may cause increased levels include calcium, cholecystokinin, epinephrine, glucagon, pentagastrin, and oral contraceptives.

Procedure and patient care

 • See inside front cover for Routine Blood Testing.

• Fasting: yes

• Blood tube commonly used: green or red

 • Collect a venous sample of blood in a heparinized green-top tube or a chilled red-top tube according to the laboratory’s protocol.

• The specimen should be placed on ice immediately. The blood may be frozen and sent to a reference laboratory.

* Tell the patient that results may not be available for several days.

Abnormal findings

Increased levels

- Medullary carcinoma of the thyroid

- C-cell hyperplasia

- Oat cell carcinoma of the lung

- Breast carcinoma

- Pancreatic cancer

- Primary hyperparathyroidism

- Secondary hyperparathyroidism because of chronic renal failure

- Pernicious anemia

- Zollinger–Ellison syndrome

- Alcoholic cirrhosis

- Thyroiditis