Extracellular calcium ion concentration is tightly regulated through the actions of parathyroid hormone (PTH) on kidney and bone (Fig. 4.5.1). The intact peptide is secreted by the parathyroid glands at a rate that is appropriate to and dependent upon the prevailing extracellular calcium ion concentration. The causes of hypocalcaemia (Box 4.5.1) can be classified according to whether serum PTH concentrations are low (that is hypoparathyroid disorders) or high (that is disorders associated with secondary hyperparathyroidism) (1–6). The most common causes of hypocalcaemia are hypoparathyroidism, a deficiency or abnormal metabolism of vitamin D, acute or chronic renal failure, and hypomagnesaemia. This chapter will initially review the clinical features and management of hypocalcaemia, and then discuss the specific hypocalcaemic disorders.
