Blood urea nitrogen concentrations in low-birth-weight preterm infants during parenteral and enteral nutrition

OBJECTIVES: Early amino acid administration has been recommended in preterm neonates to avoid protein catabolism. In the present work, blood urea nitrogen (BUN) was used to evaluate the quantity of protein intake in preterm infants. The aim of the study was to investigate the relation between protein intake and BUN during the entire duration of parenteral and enteral nutrition. PATIENTS AND METHODS: We conducted a prospective, longitudinal, observational study. BUN was assessed in 92 preterm newborns on days 2, 5, and 15 of parenteral nutrition, on the day when infants consumed 160 mL/kg of milk, and at 36 weeks of postmenstrual infants'' age. Protein intakes were calculated from the 24-hour period preceding the time the BUN specimens were collected. The effects of gestational age and protein intakes on BUN concentrations during parenteral nutrition were ascertained by multiple regression analyses. The relation between BUN and protein intakes during enteral feeding was evaluated by a simple correlation analysis. RESULTS: Using linear regression analyses, gestational age showed a significant negative correlation with BUN concentrations during parenteral nutrition, whereas protein intakes at 2, 5, and 15 days did not correlate with BUN. A moderately positive correlation between BUN and protein intake was found when the infants consumed 160 mL/kg of milk and at 36 weeks of postmenstrual age (r = 0.5, P = 0.001 and r = 0.49, P = 0.012, respectively). CONCLUSIONS: In the early postnatal period, high BUN could be the effect of many factors other than amino acid intolerance. In contrast, BUN may represent a useful index in monitoring the adequacy of protein intake during enteral nutrition.