Disorders of Calcium Metabolism: Hypocalcemia and Hypercalcemia

Calcium (Ca(+2)) is a divalent cation that plays a critical role in numerous body functions such as skeletal mineralization, signal transduction, nerve conduction, muscle contraction, and blood coagulation. Ca(+2) metabolism is linked to magnesium (Mg(+2)) and phosphate metabolism. Ca(+2 )homeostasis is dependent on intestinal absorption, bone turnover, and renal reabsorption. The hormonal regulators of these processes are the parathyroid hormone (PTH), calcitriol {1,25-dihydroxyvitamin D [1,25(OH)(2)D]}, and serum ionized Ca(+2). Cloning of the Ca(+2)-sensing receptor (CaSR) has greatly advanced the understanding of Ca(+2) metabolism. Disorders of Ca(+2) metabolism are easily recognized because Ca(+2) is included in routine chemistry panels. Measurement of ionized Ca(+2) is the preferred way to ascertain the diagnosis of hypocalcemia and hypercalcemia.