Calcium Metabolism and Hyper and Hypoparathyroidism

Calcium balance refers to the state of calcium body stores which are primarily in bone, determined largely as a function of dietary intake, intestinal absorption, renal excretion, and bone remodeling. Calcium homeostasis refers to the hormonal regulation of serum ionized calcium concentrations by parathyroid hormone (PTH), the release and effect of which is dependent on the availability of 1,25-dihydroxyvitamin D, and levels of serum ionized calcium, which together regulate calcium absorption and transport in the tissues of the gut, kidney, and bone. Primary hyperparathyroidism is diagnosed on the basis of a raised PTH level in the presence of hypercalcemia. Hypoparathyroidism refers to the failure of the body to produce levels of PTH sufficient to maintain a normal level of serum calcium. Pseudo-parathyroidismis characterized by end-organ resistance to PTH which presents as hypocalcemia and hyperphosphatemias under high PTH levels.