Calcium and phosphorus are important body minerals. They form the mineral component of bones, and they exist as charged particles called ions in the blood and inside cells. Parathyroid hormone (PTH) regulates the amount of calcium and phosphorus in bone and blood. PTH is made by four small parathyroid glands located in the neck behind the thyroid gland. Hypoparathyroidism occurs when there is too little PTH. Blood calcium levels fall, and phosphorus levels rise. The most common cause of hypoparathyroidism is injury to the parathyroid glands during head and neck surgery. Rarely, hypoparathyroidism is a side effect of radioactive iodine treatment for hyperthyroidism. PTH secretion also may be impaired when blood levels of magnesium are low, or when blood pH is too high, a condition called metabolic alkalosis. DiGeorge syndrome is a childhood disease in which hypoparathyroidism occurs due to a total absence of the parathyroid glands at birth. Familial hypoparathyroidism occurs with other endocrine diseases, such as adrenal insufficiency, in a syndrome called type I polyglandular autoimmune syndrome (PGA I). The risk factors for hypoparathyroidism include recent thyroid or neck surgery, a family history of parathyroid disorder, or certain autoimmune endocrine diseases, such as Addison's disease. | 
Endocrinology
