The most frequent cause of hypocalcemia is a low albumin level, but if serum ionized (free) calcium is normal, then no disorder of calcium metabolism is present and no treatment is needed. Causes of low ionized calcium, which is needed for enzymatic reactions and neuromuscular function, include renal failure, hypoparathyroidism, severe hypomagnesemia, hypermagne-semia, and acute pancreatitis. It is also associated with thyroidectomy and radical neck dissection when there is postoperative ischemia to the parathyroids.

Low serum calcium levels can also occur after small bowel resection, partial gastrectomy with gastrojejunostomy, and Crohn's disease. Severe diarrhea or laxative abuse may also cause hypocalcemia; when intestinal surfaces are lost, less calcium is absorbed. A transient low calcium level can result from massive administration of citrated blood. Some drugs that can result in hypocalcemia include loop diuretics, phenytoin, phosphates, caffeine, alcohol, antimicrobials (pentamidine, ketoconazole, aminoglycosides), antineoplastic agents (cisplatin, cytosine arabi-noside), and corticosteroids.

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