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What is hyperparathyroidism and what causes it?

The parathyroid glands make a hormone that tells the body how much calcium to store in the bones and how much to have in the blood. Sometimes parathyroid glands enlarge and send out too much parathyroid hormone (PTH). This is called hyperparathyroidism. When this happens, there is too much calcium in the blood and not enough in the bones. This can cause the bones to become weak and can lead to fractures. If there is too much calcium in your blood, the kidneys will try to excrete it in the urine and this may cause increased urine output, kidney stones, or even kidney damage.

Hyperparathyroidism occurs in about 1% of the general population and up to 2% of the elderly population. It is more common in woman than in men.

There are three forms of hyperparathyroidism, which include:

The most common form of hyperparathyroidism. We do not know exactly why people get it. In 80-85 percent of cases, this is due to a parathyroid adenoma or enlargement of a single gland.

Seen most often in people with kidney disease, gastrointestinal calcium malabsorption, and vitamin D deficiency. All four parathyroid glands are enlarged.

Occurs in people with a history of kidney disease who then receive a kidney transplant. Most patients have an enlargement of all four glands, but some may only have enlargement of one or two glands.


Figure 1 illustrates a single enlarged parathyroid gland, or a single adenoma. Figure 2 illustrates two enlarged glands, and Figure 3 illustrates four gland hyperplasia. Copyright © 2016 The Board of Regents of the University of Wisconsin System