Plasma Amino Acid Concentrations in 108 Children Receiving a Pediatric Amino Acid Formulation as Part of Parenteral Nutrition

Abstract

Plasma amino acid (PAA) levels can be largely normalized during parenteral nutrition (PN) in infants and children using a pediatric-specific amino acid (AA) formulation. However, these previous results were based on individual clinical studies of small populations of neonates and infants. We have now examined AA levels in 108 children (0-7 years of age) receiving a pediatric-specific AA formulation in PN using a single analytical methodology. Infants and children were enrolled in specific protocols and parents/caregivers gave informed consent. Patients were stable and receiving age-appropriate intakes of AA and non-protein calories. Samples were obtained between 8 and10 am, processed immediately, deproteinized, and AA concentrations (μmol/L) were determined on a Beckman 6300 analyzer. Means and SD were calculated for sub-populations stratified by age: 0-1 month (48 patients, n=139), 1-6 months (36 patients, n=124), 7-12 months (11 patients, n=41), and 1-7 years (13 patients, n=51). Z scores were calculated for each amino acid [(observed mean - normal control mean)/normal control SD]. When compared to the neonatal reference range, nonessential AA had Z scores that ranged from -1.84 (asparagine) to +1.48 (threonine). Only plasma free cystine, free tyrosine, and phenylalanine had Z scores outside the -2.0 to +2.0 range (95% confidence limits). Plasma free cystine values were low in all groups except neonates. Free tyrosine levels were low in all groups despite the presence of N-acetyl-L-tyrosine in the pediatric AA formulation. Phenylalanine levels were elevated only in neonates. When children 1 to 7 years old were compared with an age-matched reference range, plasma free cystine values were low (Z score -2.47), as were plasma glutamine values (-3.11), but elevations were found in the dicarboxylic amino acids aspartic acid (+2.5) and glutamic acid (+4.27). Regardless of reference range used for comparison, all essential amino acids, except phenylalanine in neonates, were within range (-2 to +2 of the 95% confidence limits). While most AAs were within the normal range, formulation modifications are needed to normalize free cystine in infants and young children, free tyrosine in all children, and phenylalanine in neonates. The decrease in glutamine concentrations in older children has been noted by our group before, and may imply limited ability to convert glutamic acid to glutamine, or increased consumption of glutamine. In either case, increased concentrations of glutamine in older children, especially those receiving home parenteral nutrition, should be considered.