Acid-Base and Electrolyte Disorders: Calcium Disorders.

Calcium is an essential element for normal physiologic function. Normal serum calcium is maintained within a close range of 8.4 to 10.4 mg/dL, and acute or severe changes can result in serious cardiac, musculoskeletal, and neurologic consequences. Normal calcium levels are maintained by interactions of parathyroid hormone and vitamin D. Parathyroid hormone regulates calcium levels via bone resorption, renal calcium reabsorption, and enhanced calcium absorption in the small intestine. Causes of hypocalcemia include hypoparathyroidism (often postsurgical), severe chronic kidney disease, and vitamin D deficiency. Laboratory testing for serum parathyroid hormone, kidney function, vitamin D metabolites, and serum phosphorus can help differentiate among causes. Acutely symptomatic patients require inpatient treatment with intravenous calcium gluconate, cardiac monitoring, and correction of hypomagnesemia. Hypercalcemia is most often due to primary hyperparathyroidism or malignancy. In the evaluation, hypercalcemia should first be confirmed by measurement of ionized calcium or repeat measurement of total serum calcium and correction for albumin. Obtaining a serum parathyroid hormone level is the next step. Asymptomatic, chronic mild hypercalcemia is often caused by primary hyperparathyroidism, which can be observed or treated surgically. Patients with severe hypercalcemia may have profound dehydration and require inpatient treatment with intravenous fluids, bisphosphonates, and calcitonin.