CALCIUM

Abnormalities in serum calcium concentration may have profound effects on neurological, gastrointestinal, and renal function. Maintenance of the normal serum calcium is a result of tightly regulated ion transpo rt by the kidney, intestinal tract, and bone, mediated by calcaemic ho rmones especially parathyroid hormone and 1,25-dihydroxyvitamin D-3. A bnormalities in calcium transport that result in uncompensated influx into, or efflux from, the extracellular fluid, will result in hypercal caemia or hypocalcaemia, respectively. When possible the biologically important ionised calcium concentration should be measured. A variety of common disorders are responsible for abnormalities in the serum cal cium. Treatment of both hypercalcaemia and hypocalcaemia is dependent on the underlying disorder, the magnitude of the deviation of the seru m calcium, and the severity of symptoms. Fortunately, in the case of h ypercalcaemia, there is a broad selection of effective medications, es pecially the bisphosphonates. Treatment of hypocalcaemia relies on the provision of calcium and often vitamin D. In this article we review t he mechanisms responsible for abnormalities in calcium homoeostatisis, the differential diagnosis of hypercalcaemia and hypocalcaemia and ap propriate therapy.