Nitrogen deposition in malnourished children with cystic fibrosis

To determine the protein nutritional status of 21 malnourished children with cystic fibrosis (CF), total body nitrogen (TBN) was measured and the results were compared with 21 control subjects. CF patients demonstrated a lower TBN (P less than 0.001). When matched for height (n = 10) or bone age (n = 13), the CF patients still had a depressed TBN/height or TBN/lean body mass (P less than 0.05). To assess nitrogen deposition during nutritional rehabilitation, repeat TBN measurements were performed on the 21 CF patients. Nitrogen deposition ranged from -230 to 550 g/y and correlated with weight velocity (r = 0.78, P less than 0.001). Increased nitrogen deposition (greater than 150 g/y) was generally associated with normal height gain (height velocity SD score greater than -2.00) and weight gain (greater than 2.0 kg/y). Decreased nitrogen deposition was associated with poor weight gain but did not preclude normal linear growth. These data suggest an important role for TBN estimations in defining protein nutritional status in children and indicate that skeletal growth can continue in the presence of minimal nitrogen deposition.