Plasma amino acid ratio as an index of hepatocellular maturity in the neonate.

A preprandial plasma amino acid molar ratio [(isoleucine + leucine + valine)/(tyrosine + phenylalanine)] has been studied in 33 neonates of mean gestation approximately 34 weeks. 19 infants were fed a formula containing 2.5 protein/dl with a high casein content (group 1), whilst 14 received milk of 1.8 g protein/dl largely derived from whey. Although total amino acid levels were significantly higher in group 1 (p less than 0.001), the amino acid molar ratio was similar in each group. This ratio correlated directly with gestational age (r = +0.76; p less than 0.001) which, on multiple regression analysis, accounted for 57% of its variability. The effects upon the ratio of infant's sex, cholestasis, and hepatic enzyme induction are also discussed.