The nitrogen balance revisited

Nitrogen balance studies are useful tools in determining the adequacy of nutritional support regimens. Several cautions should be taken when performing these studies. 1. Urine collection should be performed thoroughly, ie, no specimens can be lost. 2. When calculating N(in), the assumption that 16% of protein by weight is comprised of nitrogen does not hold for all parenteral amino acid solutions. 3. When clculating N(out), the newer fudge factors developed by Shaw-Delanty, et al, may be superior to the older values proposed by Wilmore and Blackburn. 4. When calculating nitrogen balance, change in total body urea nitrogen may become significant and should be calculated when the BUN changes by more than 5 mg/dl during the collection period. 5. Even the most meticulously performed nitrogen balance study in the clinical setting is not extremely accurate; nitrogen balance data sould always be used in combination with weight changes, wound healing, and other clinical status indicators in making changes in nutritional support regimens.