Disorders of plasma calcium

The extracellular calcium ion concentration is tightly regulated through the actions of parathyroid hormone (PTH) and vitamin D (1,25-dihydroxyvitamin D) on bone, kidney, and intestines. Abnormalities in these homeostatic mechanisms may lead to increased or decreased serum calcium concentrations, resulting in hypercalcaemia or hypocalcaemia, respectively. Hypercalcaemic disorders may be further divided into those associated with a high/high-normal serum PTH level, and those associated with a low serum PTH concentration. Hypocalcaemia occurs when abnormalities in the physiological regulation of PTH and vitamin D results in calcium levels lower than the desired normal range. Failure of release of calcium from bone, and increased binding of calcium in the circulation, are other factors causing hypocalcaemia. This chapter discusses hypercalcaemia and hypocalcaemia, exploring definitions of the diseases, their etiologies, typical and uncommon symptoms, demographics, natural history, complications, diagnostic approaches, other diagnoses that should be considered, prognosis, and treatment.