Parathyroid hormone (PTH, parathormone) is secreted by the parathyroid glands in response to decreased levels of circulating calcium. Actions of PTH include (1) mobilizing calcium from bone into the bloodstream, along with phosphates and protein matrix; (2) promoting renal tubular reabsorption of calcium and depression of phosphate reabsorption, thereby reducing calcium excretion and increasing phosphate excretion by the kidneys; (3) decreasing renal secretion of hydrogen ions, which leads to increased renal excretion of bicarbonate and chloride; and (4) enhancing renal production of active vitamin D metabolites, causing increased calcium absorption in the small intestine. The net result of PTH action is maintenance of adequate serum calcium levels.

Note: PTH is measured by radioimmunoassay. Because the antibody used for the assay directly affects the results, values vary according to the laboratory performing the test.

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

• Suspected hyperparathyroidism:
  • Elevated levels occur in primary hyperparathyroidism as a result of hyperplasia or tumor of the parathyroid glands.
  • Elevated levels also may occur in secondary hyperparathyroidism (usually as a result of chronic renal failure, malignant tumors that produce ectopic PTH, and malabsorption syndromes).
• Suspected surgical removal of the parathyroid glands or incidental damage to them during thyroid or neck surgery, as indicated by decreased levels
• Evaluation of parathyroid response to altered serum calcium levels, with elevated serum calcium levels, especially those resulting from malignant processes, leading to decreased PTH production
• Evaluation of parathyroid response to other disorders that may lead to decreased PTH production (e.g., hypomagnesemia, autoimmune destruction of the parathyroid glands)⁵¹

Nursing Care Before the Procedure

Client preparation is essentially the same as that for any study involving 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.

A venipuncture is performed and the sample collected in a red-topped tube. A sample for serum calcium also may be obtained. The sample(s) should be handled gently to avoid hemolysis and transported promptly to the laboratory.

Nursing Care After the Procedure

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

• Resume foods withheld before the test.
• Increased levels: Note and report increased levels in relation to calcium and phosphate levels. Assess for signs and symptoms of hypercalcemia (greater than 10.5 mg/dL) leading to renal calculi formation, susceptibility to fractures, sluggishness, lethargy, anorexia, and constipation. Instruct in dietary restriction of calcium, medication regimen (corticosteroids, antineoplastics, phosphates), or signs and symptoms of hypophosphatemia (less than 3 mg/dL) such as irritability, confusion, and functional deficits. Instruct in dietary intake of foods rich in phosphorus and medication replacement regimen.
• Decreased levels: Note and report decreased levels in relation to calcium levels. Assess for signs and symptoms of hypocalcemia (less than 8.5 mg/dL), such as muscle cramping and spasms of hands and feet. In mild cases, instruct in dietary intake of calcium and vitamin D supplements; in severe states, prepare for IV administration of calcium.