SERUM CONCENTRATIONS OF THYROXINE-BINDING GLOBULIN, PREALBUMIN AND ALBUMIN IN HEALTHY FULLTERM, SMALL-FOR-GESTATIONAL AGE AND PRETERM NEWBORN INFANTS

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Abstract
Simultaneous serum concentrations of thyroxine-binding globulin (TBG), prealbumin (TBPA) and albumin (Alb) were measured in 130 full-term, 32 small-for-gestational age and 25 preterm infants during their first 6 days of life. In all infants serum concentrations of TBG were higher and serum TBPA and Alb were lower than in male adults. Even higher serum TBG levels were found in the mothers. There was no correlation between serum concentrations in paired maternal and cord sera. In infants with birth weights appropriate for gestation serum TBG, TBPA and Alb concentrations increased progressively with gestational age. In small-for-gestational age infants born at term serum concentrations of TBG and Alb were lower than those in full-term, but higher than those in premature newborns. Serum TBPA in small-for-gestational age babies was even lower than seen in prematures. A positive correlation was found between thyroid hormones and TBG concentrations, not between serum TBPA and thyroid hormones. The ratios between serum concentration of thyroid hormones and proteins might indicate that more thyroid hormone binding sites are occupied in fullterm than in low birthweight newborns. The main reason for the different serum levels of thyroid hormones in full-term, small-for-gestational age and preterm babies is probably the various serum TBG concentrations demonstrated in these infants.