Excessive calcium in the blood, called hypercalcemia, usually signals that something is wrong with the parathyroid glands. The parathyroids release a chemical called parathyroid hormone (PTH), which helps maintain a normal supply of calcium in the blood, bones, and urine. If the parathyroid glands secrete too much hormone, as in hyperparathyroidism, the balance is disrupted: blood calcium rises. The bones may lose calcium, and too much calcium may be absorbed from food. The levels of calcium may increase in the urine, leading to kidney stones or kidney damage. PTH also acts to lower blood phosphorous levels by increasing excretion of phosphorus in the urine. High blood calcium can exist for many years before it is found by accident or by family screening.