Comment

• Hypercalcaemia is a far less common finding in children than in adults, but often presents difficulties when it is serendipitously identified in an otherwise asymptomatic child. Total plasma calcium is normally maintained at 2.2–2.6 mmol/l, with little variation throughout life. Approximately 40% is bound to protein, primarily albumin, while 50% is ionised and in its physiologically active form. The remaining 10% is complexed to anions. It is often expressed as a corrected value, accounting for the effect of plasma albumin on calcium level:

Ca_corrected  =  Ca_total − 0.02 (albumin − 40)

• The plasma calcium level is controlled by a complex interplay of three major components: parathyroid hormone (PTH) secretion, 1,25-dihydroxyvitamin D secretion, and the calcium-sensing receptor (CaSR). The three key organs that are involved in the maintenance of plasma calcium are the kidney, bone and the small intestine (figure 1). Thus a rise in the level of ionised calcium is detected by the CaSR located in the parathyroid glands and the renal tubules. In the parathyroid glands this leads to a reduction in the synthesis and secretion of PTH. The reduced circulating level of PTH then acts in three different ways. (1) It alters the renal tubular reabsorption of calcium in the kidney leading to less of the filtered plasma calcium being reabsorbed and more excreted in the urine. (2) There is a reduction in bone resorption leading to less calcium being released from bone into the circulation. (3) There is a reduction …