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)₂D]}, 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.