Free thyroxine values in dried blood spots on filter paper in newborns are related to both gestational age and birth body weight

Abstract

The results of free thyroxine (FT4) measurements in dried blood spots on filter paper in 744 euthyroid newborns (616 at term, 128 preterm), 10 newborns with congenital hypothyroidism and 4 euthyroid newborns with congenital TBG deficiency are reported. FT4 was measured by column adsorption chromatography of free hormone followed by radioimmunoassay in the eluate. FT4 values averaged 24 +/- 0.2 pmol/L (mean +/- SE) in euthyroid newborns, 23.0 +/- 0.9 pmol/L in euthyroid newborns with TBG deficiency (p = NS), and 5.7 +/- 0.4 pmol/L in hypothyroid newborns (p less than 0.001 vs both groups). Total T4 (TT4) values in newborns with TBG deficiency were not different from those in hypothyroid newborns, but were significantly lower than those in euthyroid newborns without TBG abnormalities. FT4 values were higher in full-term newborns than in preterm newborns (25.2 +/- 0.3 vs 21.2 +/- 0.5 pmol/L, p less than 0.001). In both full-term and preterm newborns FT4 values in dried blood spots increased with birth body weight (bbw), virtually plateauing when bbw was greater than 2,500 g. The cut-off values established on the basis of the bbw (8.0 and 13.1 pmol/L for a bbw of less than or equal to 2,500 g and greater than 2,500 g, respectively) showed higher specificity and predictive value of positive results than the cut-off values based on the gestational age. In any case, the sensitivity, specificity and predictive values of FT4 determinations proved to be higher than those of TT4 and TSH measurements.(ABSTRACT TRUNCATED AT 250 WORDS)

Infant feeding, fetal growth and adult thyroid function

“…In this group, TSH concentrations rose and FT4 concentrations fell with increasing birthweight but not with weight at 1 year of age, suggesting that an impairment of fetal rather than infant growth influenced thyroid function. These findings based on thyroid function in adults contrast with the data from several observations in both human and animal neonates that fetal growth retarda¬ tion is associated with lower FT4 and FT 3 concentrations (17)(18)(19)(20). If our data are confirmed, they would suggest that the relationships between birthweight and thyroid function are different in neonates and adults.…”

Good short-term outcomes of kangaroo mother care in infants with a low birth weight in a rural South African hospital

“…The mothers were encouraged to continue with KMC at home after discharge. 2,11,12,13,21 The infants who developed jaundice weighed statistically less and had a slower weight gain than those without jaundice. During the jaundice episode, the mothers could only partially practise KMC because the infants were under phototherapy lights.…”

“…3,7,8,9 Kangaroo mother care can also help to decrease the prevailing high levels of morbidity and mortality. 10,11,12 In South Africa, a developing country, a number of training hospitals have established separate KMC wards. Mothers of low birth weight infants were able to practise continuous KMC, which resulted in those infants being discharged from the incubator sooner than they would traditionally have been.…”

Longitudinal Assessment of Pituitary-Thyroid Axis and Adrenal Function in Preterm Infants Raised by ‘Kangaroo Mother Care’

“…17-OHP, TSH and T 4 were measured by a ‘blind’ protocol in Israel, from blood spotted on filter paper [11, 12, 13, 14, 15, 16]sampled periodically in Colombia. This enabled us to compare the maturation of the adrenal [17]and pituitary-thyroid axis, as reflected by hormonal concentrations, in infants that underwent KMC and controls.…”