Determination of the Urinary Components of Nitrogen Excretion in Premature Infants

Abstract

Background: Although several researchers have conducted nitrogen balance studies in premature infants in the past, very few have partitioned urinary nitrogen into its components. Determination of the urinary components of nitrogen excretion in premature infants will help in evaluating the ideal protein requirements for infant growth. Aims: To investigate the components of nitrogen excretion, including urea, protein, creatinine, uric acid and ammonia in premature infants. To Identify the unknown nitrogen compounds which account for the TUN. Findings from the study could have important implications for infant growth. Methods: Thirty-nine urine samples from healthy premature infants. Total urinary nitrogen of the samples was measured by a chemiluminescent nitrogen analyser. Protein, urea, uric acid, creatinine, nitrite and nitrate levels were measured using different assays. Urine samples were fractionated (e.g. acid soluble, acid insoluble, hydrophilic, hydrophobic fractions) and the nitrogen content of each fraction measured in order to elucidate the components of nitrogen excretion in urine. Results: the average UUN/ TUN ratio in preterm infants is 48.8%. Therefore, UUN cannot be used by its own to measure TUN. The average UUN/TUN ratio varies among different groups and across all samples from the same infant. By using HPLC I attempted to identify the components by comparing the retention times or peaks of samples with those of known compound. For proteins and pellets, the p value showed a significant relationship, but the r2 value did not show a strong correlation (r2 = 0.2660, p = 0.0042). Conclusion: All the data collected in the study indicates that UUN/TUN ratio is low and the ratio of UUN/TUN between samples is variable. Therefore, UUN on its own is not an accurate measurement for TUN in healthy premature infants. Underdetermined nitrogen components remain an area for further investigation.