A critical assessment of plasma alkaline ribonuclease as an indicator of protein nutritional status in infancy

Plasma alkaline ribonuclease (RNase) was measured at birth and during infancy to assess its usefulness as an indicator of protein nutritional status. Cord blood enzyme activity did not indicate intra-uterine protein malnutrition in the less well-grown babies. Differences in enzyme activity were found which related to the quality of the dietary protein fed to both preterm and term light for gestational age babies. Higher activity on day 7 in those infants fed a predominantly curd protein formula suggested that this was less well utilised than a curd and whey protein formula. Serial enzyme measurements in four infants with metabolic disease showed how the enzyme activity altered in response to changes in the quantity of dietary protein. These results are critically discussed.