Eleven plasma proteins as indicators of protein nutritional status in very low birth weight infants

Concentrations of 11 plasma proteins were measured in 28 healthy, growing, very low birth weight, appropriate-for-gestational-age infants fed varying levels of human milk protein intake (range 1.7 to 3.9 g/kg per day). Significant positive correlations were found between mean protein intake and concentrations of 7 of the plasma proteins studied (transthyretin, retinol-binding protein, and transferrin: P less than .001; vitamin D-binding protein and apolipoprotein B: P less than .01; albumin and apolipoprotein A I: P less than .05). A weak negative correlation with mean protein intake was seen for the plasma level of orosomucoid, whereas no significant correlations were found for the plasma concentrations of fibronectin and alpha 1-antichymotrypsin. Protein intake, not energy intake, constituted the main contribution to the changes in the concentrations of transthyretin, retinol-binding protein, and transferrin. The levels of plasma transthyretin and transferrin were also strongly correlated with weight and length growth of the infants during the study as well as with other indicators of protein nutritional status such as preprandial concentrations of plasma amino acids and serum and urine urea. These data indicate that of the 11 plasma proteins studied, transthyretin, transferrin, and retinol-binding protein are the most suitable to evaluate protein nutritional status in very low birth weight infants.