Amino acid-induced hypercalciuria in patients on total parenteral nutrition

Ingestion of protein is known to increase urinary calcium excretion. By studying the effect of intravenous amino acid infusion on calcium excretion, the variables of diets and intestinal absorption are avoided. Five patients on total parenteral nutrition with otherwise constant nutrient infusions containing 240 mg of calcium were randomized to two different levels of amino acid infusion. On 1 g/kg ideal body weight amino acid infusion, two patients excreted more than 240 mg of calcium in the urine, while on 2 g/kg ideal body weight amino acid infusion all five patients lost more calcium in urine than was infused. Mean urinary calcium excretion was increased from 287 to 455 mg/day. On the higher amino acid dose, mean glomerular filtration rate increased from 102 to 143 ml/min. There was no effect of amino acid dose on serum calcium, ionized calcium, parathyroid hormone, and 25 (OH) vitamin D. Calcium excretion corrected for the glomerular filtration rate was increased at the higher amino acid dose, indicating a decrease in renal calcium reabsorption. Daily urinary excretion of sulfate, ammonia, and titratable acidity were increased during the high amino acid infusion. Hypercalciuria induced by high levels of amino acid infusion during total parenteral nutrition may contribute to the development of metabolic bone disease.