Renal failure can result in diminished formation of 1, 25 (OH) 2D due to Direct renal cell damage Suppression of 1-alpha-hydroxylase (needed for the vitamin D conversion) by hyperphosphatemia Other causes Other causes of hypocalcemia include Acute pancreatitis (when lipolytic products released from the inflamed pancreas chelate calcium) Drugs, including antiseizure drugs (eg, phenytoin, phenobarbital) and rifampin, which alter vitamin D metabolism, and drugs generally used to treat hypercalcemia Hungry bone syndrome (persistent hypocalcemia and hypophosphatemia occurring after surgical or medical correction of moderate to severe hyperparathyroidism in patients in whom serum calcium concentrations had been supported by high bone turnover induced by greatly elevated PTH—hungry bone syndrome has been described after parathyroidectomy, after renal transplantation, and rarely in patients with end-stage renal disease treated with calcimimetics) Hyperphosphatemia (causes hypocalcemia by poorly understood mechanisms; patients with renal failure and subsequent phosphate retention are particularly prone) Hypoproteinemia (reduces the protein-bound fraction of serum calcium; hypocalcemia due to diminished protein binding is asymptomatic—because ionized calcium is unchanged, this entity has been termed factitious hypocalcemia) Infusion of gadolinium (may spuriously lower calcium concentration) Magnesium depletion (can cause relative parathyroid hormone deficiency and end-organ resistance to PTH action, usually when serum magnesium concentrations are < 1.0 mg / dL [< 0.5 mmol / L]; magnesium repletion increases PTH concentrations and improves renal calcium conservation) Septic shock due to suppression of PTH release and decreased conversion of 25 (OH) D to 1, 25 (OH) 2D Transfusion of > 10 units of citrate-anticoagulated blood Use of radiocontrast agents containing the divalent ion-chelating agent ethylenediaminetetraacetate (EDTA—can decrease the concentration of bioavailable ionized calcium while total serum calcium concentrations remain unchanged) Although excessive secretion of calcitonin might be expected to cause hypocalcemia, calcitonin actually has only a minor effect on serum calcium.