Serum triiodothyronine concentrations in infancy, childhood, adolescence and pediatric thyroid disorders

Applications for non-invasive thyroid hormone measurements in mammalian ecology, growth, and maintenance

Thyroid hormones (THs) play a pivotal role in the regulation of metabolic activity throughout all life stages. Cross-talk with other hormone systems permits THs to coordinate metabolic changes as well as modifications in growth and maintenance in response to changing environmental conditions. The scope of this review is to explain the relevant basics of TH endocrinology, highlight pertinent topics that have been investigated so far, and offer guidance on measuring THs in non-invasively collected matrices. The first part of the review provides an overview of TH biochemistry, which is necessary to understand and interpret the findings of existing studies and to apply non-invasive TH monitoring. The second part focuses on the role of THs in mammalian ecology, and the third part highlights the role of THs in growth and maintenance. The fourth part deals with the advantages and difficulties of measuring THs in non-invasively collected samples. This review concludes with a summary that considers future directions in the study of THs.

Blood levels of 3,5,3'-triiodothyronine and thyroxine: differences between children, adults, and elderly subjects

The serum levels of 3,5,3'-triiodothyronine (T3) and thyroxine (T4) in children, adolescents, adults, and elderly subjects have been measured by radioimmunoassays. It was found that while the T4 levels were essentially equal in all age groups examined, the T3 levels were markedly different. In children and adolescents (1-15 years), high values were recorded; indeed, they exceeded the upper normal limit in adults (20-80 years). From the age of 20, the T3 levels remained unaltered until the age of 80, after which there was a further reduction, to values approaching the lower normal limit for T3 in middle-aged subjects. The findings emphasize that separate normal values must be established for different age groups, in order to avoid diagnostic misinterpretations and therapeutic failures.

Reference range of thyroid hormones in normal Indian school-age children

OBJECTIVE

There is an ongoing debate on narrowing the TSH reference range in adults. In view of the scarce data on normal values of thyroid function tests in children from India, we planned to establish a reference range for thyroid hormones in school-age children.

DESIGN AND SUBJECTS

All children (N = 9527; 6-19 years) from six schools representing various zones of Delhi were evaluated for clinical evidence of goitre, thyroid ultrasound, serum free T3 (FT3), free T4 (FT4) and TSH and anti-thyroid peroxidase (anti-TPO) antibodies. From this sample, a reference population (N = 5122) was obtained by excluding those with a personal or family history of thyroid disease, use of thyroid medications, goitre, hypoechogenicity/nodularity on ultrasound or serum anti-TPO antibodies.

MEASUREMENTS

Thyroid hormone (FT3, FT4 and TSH) reference ranges were established for each year of life for the total and reference populations.

RESULTS

In the reference population, mean serum FT3 was in the range 4.19-4.84 pm/l for boys and 4.03-4.47 pm/l for girls, mean serum FT4 14.69-17.36 pm/l for boys and 14.32-15.88 pm/l for girls, and mean serum TSH 2.57-3.6 mIU/l for boys and 1.83-3.58 mIU/l for girls. For TSH, the 97th percentile was in the range 6.01-8.4 mIU/l for boys and 5.28-8.04 mIU/l for girls, suggesting that at least in children there may not be a need to reduce the upper limit of normal for serum TSH.

CONCLUSIONS

This study provides mean reference intervals for FT3, FT4 and TSH for each year of life for both the sexes separately using strict exclusion criteria.

Serum T4, T3 and TBG concentrations during puberty in males

Measurements of serum thyroxine (T4), thyroxine binding globulin (TBG), and triiodothyronine (T3), using RIA, were conducted in healthy Israeli boys, 149 children from the age 8 years were divided into five groups according to Tanner's puberty stages. The correlation with Tanner's staging showed a significant decrease in T4 and TBG concentrations during puberty. However, T3 decreased only toward the last stage of puberty (between P4 to P5). Our data indicate that during puberty in male subjects the decrease in TBG plays a significant role in the decrease of thyroid hormone concentrations.

Pharmacotherapy for autistic children: a summary of research

An overview of research involving pharmacotherapy in infantile autism is presented. Methodological issues relating to experimental design, rating instruments and ecological factors are considered. Classification of infantile autism and diagnostic problems are discussed. Research investigations conducted in order to define diagnostic subgroups in the etiologically heterogeneous population of autistic children are described. An attempt is made to relate biochemical findings to clinical drug response. Recent findings are presented indicating that a potent neuroleptic is able to yield simultaneously significant decrease of behavioural symptoms and improved learning under both clinical and laboratory conditions. The drug can be effective in conservative doses and administered over a period of 14 weeks without untoward effects. New research plans are introduced where attentional learning will be assessed in an operant conditioning paradigm using automated procedures.

Thyroid hormone in autistic children

Thyroid hormone plays an important role in the pre- and postnatal development and function of the central nervous system. Disturbances in thyroid hormone regulation have been hypothesized in childhood autism. We evaluated blood indices of thyroid function, including serum thyroxine, triiodothyronine, and thyroid-stimulating hormone, in a large population of autistic children. No differences were found between autistic and normal children.

Circulating thyroid hormone levels in children

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 17 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 μg/100 ml was higher than the adult mean serum T4 of 8·5±1·5 μg/100 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 oestrogen-dependent 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.

Triiodothyronine and thyroid-stimulating hormone in protein-calorie malnutrition in infants

Protein-calorie malnutrition (P.C.M.) in a group of 43 Senegalese children aged eighteen to thirty months was characterised by a sharp fall in serum-triiodothyronine (T3) concentration to 25-3% of the mean value in healthy age-matched controls. This decrease in T3 was significantly (P less than 0-001) more pronounced in kwashiorkor of recent onset than in long-term P.C.M., a finding which suggests that impaired thyroxine (T4) monodeiodination in the liver was responsible for the fall in serum-T3 concentration rather than a reduction in the secretion of T3 by the thyroid. Serum-T3 concentrations became normal in both malnourished groups after two weeks of appropriate nutrition. Serum-T3 concentrations in healthy, euthyroid, Senegalese children were higher than in White children. In frank kwashiorkor in Senegalese children, serum-thyroid-stimulating-hormone (T.S.H.) concentrations were within the normal range throughout the entire course of dietary therapy, indicating that the children remained euthyroid. In contrast, protracted P.C.M. led to impairment of the T.S.H./T3 feedback mechanism and to a condition resembling hypophysectomy, which required two weeks' dietary therapy for its correction.