Calcitonin

Calcitonin, also called thyrocalcitonin, is secreted by the parafollicular or C cells of the thyroid gland in response to elevated serum calcium levels. Its role is not completely understood, but the following functions are known: (1) It antagonizes the effects of parathyroid hormone and vitamin D, (2) it inhibits osteoclasts that reabsorb bone so that calcium continues to be laid down and not reabsorbed into the blood, and (3) it increases renal clearance of magnesium and inhibits tubular reabsorption of phosphates. The net result is that calcitonin decreases serum calcium levels.

Reference Values ⬆ ⬇

	Conventional Units	SI Units
Men	<0.155 ng/mL	<0.155 µg/L
Women	<0.105 ng/mL	<0.105 µg/L

Interfering Factors ⬆ ⬇

Failure to fast from food for 8 hours before the test may alter results.

Indications ⬆ ⬇

Support for diagnosing medullary carcinoma of the thyroid gland is indicated by elevated calcitonin levels, when serum calcium levels are normal. (Further verification may require raising the serum calcium level by IV infusion of calcium or pentagastrin and measuring the level to which plasma calcitonin rises in response; a rise of 0.105 to 0.11 ng/mL is to be expected.)
Altered serum calcium levels of unknown etiology may be caused by a disorder associated with altered calcitonin levels.
Elevated calcitonin levels are seen in cancers involving the breast, lung, and pancreas as a result of ectopic calcitonin production by tumor cells.
Elevated calcitonin levels also are seen in primary hyperparathyroidism and in secondary hyperparathyroidism resulting from chronic renal failure.

Care Before Procedure ⬆ ⬇

Nursing Care Before the Procedure

Client preparation is essentially the same as that for any study involving the collection of a peripheral blood sample (see Appendix I).

For this test, the client should fast from food for at least 8 hours before collection of the sample.

Procedure ⬆ ⬇

A venipuncture is performed and the sample collected in a green-topped tube. The sample should be handled gently to avoid hemolysis and transported promptly to the laboratory.

Care After Procedure ⬆

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving collection of a peripheral blood sample.

Resume foods withheld before the test.
Complications and precautions: Note increased levels. Assess in relation to calcium and parathyroid hormone levels. Prepare the client for subsequent treatment decisions (medication protocol, surgery).