Hyperparathyroidism is the abnormally high production of the hormone by the four parathyroid glands, which are located near the thyroid. This elevation of the parathyroid hormone or PTH is responsible for the excessive presence of calcium in the blood, hypercalcemia. Hyperparathyroidism is due in most cases to the excessive operation of these glands, the result of the development of an adenoma. It can also be a side-effect of chronic renal failure or certain medications. Hyperparathyroidism can lead to osteoporosis and increases the frequency of urinary stones. It is diagnosed by a blood test by measuring parathyroid hormone.