Calcium levels in serum are used in Diagnosis and monitoring of a wide range of disorders including diseases of bone, kidney, parathyroid gland, or gastrointestinal tract. Hypocalcemia is due to the absence or impaired function of the parathyroid glands or impaired vitamin-D synthesis. Chronic renal failure is also frequently associated with hypocalcemia. Hypercalcemia is brought about by increased mobilization of calcium from the skeletal system or increased intestinal absorption. Calcium levels may also reflect abnormal vitamin D or protein levels.