What is a Parathyroid Hormone?

The parathyroid glands of the human body secrete parathyroid hormone (PTH), a protein consisting of amino acids. PTH regulates calcium and phosphorus amounts throughout the body and maintains a healthy balance between these minerals. Parathyroid hormone controls calcium metabolism including the absorption of calcium in the gastrointestinal tract, the amount of calcium released from bones, and the elimination of calcium through urination. Increased PTH secretion raises the level of calcium in a person’s blood. Higher blood calcium levels in turn cause a reduction in the amount of hormone that the parathyroid glands secrete into the bloodstream.

Calcium is important for bone strength and development of healthy bones and teeth. Proper muscle and nerve functioning depend on calcium. All body tissues contain phosphorus and depend on a proper balance of calcium and phosphorus.

The human body has four parathyroid glands that are in the front portion of the lower neck on the surface of the thyroid gland. Each of these parathyroid glands is about the size of a pea. Some people are born with parathyroid glands that lodge in the thymus or in the thyroid gland.

Hyperparathyroidism is a condition that causes the parathyroid glands to excrete unusually high amounts of a parathyroid hormone and is often due to a parathyroid tumor. High levels of PTH from this medical disorder cause excessive calcium loss from bones and produce high calcium levels in the body. Hypoparathyroidism is a disorder that causes the parathyroid glands to excrete insufficiently low amounts of parathyroid hormone and often results from diseased parathyroid glands or surgical removal of these glands. People with this disorder may develop dangerously low calcium levels and are usually treated with calcium supplementation.

A PTH blood test is a laboratory test that measures the amount of parathyroid hormone in a patient’s blood. Usually, a health care provider draws a blood sample from a patient’s arm and sends the sample to a testing laboratory for analysis. A patient’s physician receives the test results from the laboratory and shares the results with the patient.

Patients may obtain PTH test results with abnormally high blood levels of parathyroid hormone due to several medical conditions, including chronic kidney failure, a vitamin D deficiency, or rickets. Women who are pregnant or breastfeeding may develop high PTH levels in their blood. High PTH levels have been reported as a side effect of several drugs, including diuretics, anticonvulsants, and phosphates. PTH test results that show low blood levels of parathyroid hormone can be caused by toxic levels of vitamin D, radiation of the parathyroid glands, and excessive consumption of dietary calcium.

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