Reliability of the twenty-four-hour nitrogen balance in parenterally fed newborn infants

The reliability of shorter nitrogen balance determinations was evaluated in order to facilitate the nutritional assessment of parenterally fed infants. The intraindividual day-to-day variations of nitrogen intake, excretion, and retention were analyzed in 23 parenterally fed newborn infants (birth weight: 785-2630 g). Nitrogen retentions measured over 3 consecutive days were highly correlated (r = 0.90-0.96), and the reliability for a single 24-hr collection was estimated by r1 = 0.93. Nitrogen balance data obtained over a 24-hr period are reliable for the purpose of clinical investigations, provided the nutrient intake is constant.