HYPERCALCAEMIA DEFINITION Abnormally high concentration of calcium in the blood (serum calcium > 2.58 mmol/L or > 10.3 mg/dL). The ionized calcium is a more accurate reflection of calcium status, especially in patients with low serum albumin. The normal ionized calcium is 1.12 to 1.23 mmol/L (4.48 to 4.92 mg/dL). TOXIC CAUSES Hypercalcaemia is observed most often in chronic intoxications and is a consequence of one or more of the following mechanisms: Increased bone resorption of calcium Increased intestinal resorption of calcium Impaired renal excretion of calcium Most frequent causes: Vitamin D overdose Milkalkali syndrome (Burnett syndrome) Calcium salts intoxication Occasional causes: Theophylline Thiazide diuretics NON-TOXIC CAUSES Hyperparathyroidism Some neoplasms and bone metastases CLINICAL FEATURES Mild hypercalcaemia may be asymptomatic. Moderate to severe toxicity may cause constipation, anorexia, abdominal cramps, nausea, vomiting, polyuria, polydipsia, dehydration, delirium, stupor, psychotic states, asthenia, muscular weakness, shortening of QT interval on the ECG, and cardiac arrest. Acute renal failure may result from calcium deposition in the kidney. RELEVANT INVESTIGATIONS Total serum calcium and ionized serum calcium Other serum electrolyte concentrations including magnesium, phosphate, sodium, and potassium Renal function (creatinine, urea) Electrocardiograph (QT interval) DIFERENTIAL DIAGNOSIS Other causes of coma and metabolic encephalopathy Polyuria and dehydration from diabetes insipidus or diabetes mellitus TREATMENT Cease administration of, or exposure to, the causative agent. Correct dehydration by administering intravenous fluids. To promote calcium excretion, administer intravenous normal saline (3 to 4 L/day in adults). Furosemide (20 to 80 mg IV in adults) may be given following correction of hypovolaemia. Monitor urine output and match renal losses with additional intravenous fluids. Corticosteroids: Prednisone (1 mg/kg orally) or hydrocortisone (300 mg intravenously) is recommended for patients with hypercalcaemia caused by Vitamin D overdose. Calcitonin (5 to 10 units/kg IM every 8 hours) promotes calcium uptake in bone, and is mainly used in patients with severe hyperparathyroidism. Haemodialysis may be indicated if renal failure develops. CLINICAL COURSE & MONITORING Urine output and fluid and electrolyte balance Serum calcium and ionized calcium concentration Renal function Electrocardiogram (QT interval) LONG-TERM COMPLICATIONS Hypercalcaemia by itself may cause nephrocalcinosis and/or renal insufficiency AUTHOR/REVIEWERS Author: Dr V. Danel, Unité de Toxicologie Clinique, Grenoble, France. Peer Reviewers: Cardiff 9/96: V. Afanasiev, M. Burger, T. Della Puppa, L. Fruchtengarten, K. Olsen, J. Szajewski.