Protein quantity and quality in term and preterm infants: effects on urine creatinine and expression of amino acid excretion data.

The effect of dietary protein quantity and quality on the excretion of creatinine in preterm and term neonatal infants has been investigated. Whey protein predominant formulas result in increased creatinine excretion as compared with either casein protein predominant formulas or with pooled human milk in preterm infants (p less than 0.001 by ANOVA). The volume of human milk (170 versus 185 versus 200 ml/kg/day) appears to have little effect in these infants. In term infants, few differences among the feeding groups were observed, although creatinine excretion did increase with time. The pattern of creatinine excretion among feeding groups was similar regardless of whether or not the data were expressed in milligrams per deciliter or in milligrams per 24 hours. Small correlations of creatinine excretion with birth weight were observed, but these appeared to vary, depending on the type of feeding. These diet-induced differences in creatinine excretion indicate the need for caution in expressing other urinary metabolites, such as amino acids, relative to creatinine excretion.