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Parathyroid Hormone
About this test
A parathyroid hormone (PTH) blood test measures the level of parathyroid hormone in the blood. This test is used to help identify hyperparathyroidism or to find the cause of abnormal calcium levels. PTH controls calcium and phosphorus levels in the blood.
PTH is
made by the
parathyroid glands 
, which are four pea-sized glands
that lie behind the
thyroid gland. If the blood calcium level is too low,
the parathyroid glands release more PTH. This causes the bones to release more
calcium into the blood and reduces the amount of calcium released by the
kidneys into the urine. Also,
vitamin D is converted to a more active form, causing
the intestines to absorb more calcium and phosphorus. If
the calcium level is too high, the parathyroid glands release less PTH, and the
whole process is reversed.
PTH levels that are too high or too low can cause problems with the kidneys and bones and cause changes in calcium and vitamin D levels.
Tests for calcium and phosphorus levels in the blood may be done at the same time as a PTH test.
| By: | Healthwise Staff | Last Revised: April 21, 2010 |
| Medical Review: | E. Gregory Thompson, MD - Internal Medicine Matthew I. Kim, MD - Endocrinology | |
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