Circulating thyroid hormone levels in children

Abstract

SUMMARY Extensive use of radioimmunoassay for routine measurement of serum thyroid hormones in paediatric thyroid disorders showed inconsistencies between laboratory results based upon adult criteria and clinical observation. To resolve this disparity, serum triiodothyronine (T3) and thyroxine (T4) levels were measured by radioimmunoassay in 354 healthy children aged between 3 weeks and 1 7 years.The mean serum T3 concentration in children up to 10 years of age was 1 94±0*35 ng/ml (SD) which was higher than the mean serum T3 of 1-37±0 25 ng/ml in healthy adults. Similarly, the mean serum T4 of 10±2-5 ,tg/100 ml was higher than the adult mean serum T4 of 8-5±1 5 ,ug/l00 ml. Neither concentration changed significantly from 3 weeks to 10 years of age, nor was there any sex difference. In girls serum T3 and T4 concentrations declined gradually from age 10 to maturity. A perimenarcheal nadir observed in the T4 data was thought to reflect the joint effects of the age-dependent fall in circulating T4 and the concomitant oestrogendependent rise in thyroxine-binding globulin. In boys the decline in serum T3 occurred approximately 2 years later than in the girls. These observations show that the normal ranges for serum T3 and T4 in children are higher than those in adults and that reference to normal adult ranges may lead to misclassification in diagnosis and monitoring of paediatric thyroid disorders.Simple and rapid radioimmunoassays for measurement of serum thyroxine (T4) and triiodothyronine (T3) are now readily available for assessment of thyroid function in children, yet the criteria for normal thyroid function are mostly derived from adult data (Fisher, 1973). Using a competitive protein binding assay, O'Halloran and Webster (1972) reported that after the neonatal surge in thyroid hormone concentration, serum T4 declined till the age of one year to stabilize at a mean level of 9-2 Fg/100 ml. Murray et al. (1971) showed higher serum T4 and T3 resin uptake levels in childhood which declined slowly with age until late adolescence. Published information on circulating T3 levels is, however, sparse and conflicting. AvRuskin et al. (1973) found no significant change in six groups of children aged between 1 and 18 years, the mean serum T3 levels being within the normal adult range. By contrast, Rubenstein et al. (1973) reported higher serum T3 levels in young children with a fall of approximately 0 05 ng/ml per decade.After extensive routine use of serum T3 estimations, it has become apparent that circulating T3 levels in children are higher than in adults, and that many clinically hypothyroid children with raised serum thyroid-stimulating hormone (TSH) levels Received 18 February 1977 have T3 levels within the normal adult range. This study was undertaken to determine serum T3 and T4 levels in normal children from 3 weeks to 17 years of age. Subjects and methodsSera were obtained for estimation of T3, T4, and TSH concentrations in the following groups of children.( 1)

Thyroid hormone concentrations in relation to age, sex, pregnancy, and perinatal loss in bottlenose dolphins (Tursiops truncatus)

“…Similarly, in several species of terrestrial mammals, thyroid hormone concentrations appear to be higher in younger than older dogs (Reimer et al 1990), cats (Skinner, 1998), and goats (Colavita et al, 1983). Although the basis for the age-related effects of thyroid hormones in managed care dolphins is not known, it is well known that thyroid hormones support early childhood development and maturation in humans (Corcoran et al, 1977;Croughs et al, 1965) and appear to be necessary for adapting to extreme or changing environmental conditions as found in wild pinniped pups and other wild marine mammals (Engelhardt and Ferguson, 1980;Fair et al, 2011;Haulena et al, 1998;Porterfield and Stein, 1994;Stokkan et al, 1995;Woldstad and Jenssen, 1999). Nonetheless, the present results combined with previous results in wild dolphins and other mammalian species provides support for an age-related (juvenile to adult) decrease in thyroid hormone concentrations in female and male bottlenose dolphins.…”

A longitudinal study of total and free thyroid hormones and thyroxinebinding globulin during normal puberty

“…Several groups have reported changes in total thyroid hormone and binding protein level during childhood (4)(5)(6), but it is likely that changes in the free hormone concentrations of T3 and T4 are more pertinent to normal growth and develop¬ ment. Some investigators have extrapolated free hormone concentrations from total thyroid hor¬ mone and binding protein levels (7,8), but the more recent direct methods of free hormone measure¬ ment have only been applied in one study reported by Butler et al (9).…”

Leptin and thyroxine during sexual development in male monkeys: effect of neonatal gonadotropin-releasing hormone antagonist treatment and delayed puberty on the developmental pattern of leptin and thyroxine secretion

“…While there is general agreement that circulating levels of thyroid hormones decline throughout adolescence (25,26), the relationship between thyroid status and pubertal development is not clear. Corcoran and colleagues (27) reported that there was a peripubertal nadir in circulating levels of thyroid hormones in children, although it occurred 2 years later in boys than in girls. In another crosssectional study in children in which data from boys and girls were combined, there was a transient increase in thyrotropin secretion and a resultant rise in T4 and tri-iodothyronine (T3) that preceded clinical pubertal changes (28).…”