[Hypercalcaemia: intensive care or general ward]

Hypercalcaemia is a life-threatening electrolyte imbalance, which not only occurs in the context of an endocrinological disease but is also frequently associated with a tumour. Its severity is determined by the level of deviation from normal, acuity of occurrence, and severity of the symptoms. These are unspecific, can affect any organ system and ultimately result in a life-threatening hypercalcaemic crisis characterised by cardiac arrhythmia, metabolic acidosis, exsiccosis, fever, psychotic states and, ultimately, coma. Endocrinological disorders, drugs such as vitamin D3, vitamin A, checkpoint inhibitors, but also malignancies can be causative for the development of hypercalcaemia. Up to 30% of tumour patients are affected by hypercalcaemia. It is associated with a poor prognosis and a high tumour burden. Malignant hypercalcaemia is mainly caused by PTHrP (parathormone-related peptide), which is secreted by the tumour cells. In oncological patients, serum calcium (ionised calcium and non-ionised calcium) should be evaluated regularly. As the level of serum calcium depends on the albumin concentration, the latter should also be evaluated. Treatment consists of increasing the intravasal volume, increasing calcium excretion and inhibiting calcium reabsorption.