Abstract
BackgroundAge- and sex-specific reference intervals are an important prerequisite for interpreting thyroid hormone measurements in children. However, only few studies have reported age- and sex-specific pediatric reference values for TSHbasal (TSH), free T3 (fT3), and free T4 (fT4) so far. Reference intervals are known to be method- and population-dependent. The aim of our study was to establish reference intervals for serum TSH, fT3, and fT4 from birth to 18 years and to assess sex differences.Methods2,194 thyroid hormone tests obtained from a hospital-based pediatric population were included into our retrospective analysis. Individuals with diagnoses or medications likely to affect thyroid function were primarily excluded, as well as the diagnostic groups, if different from the purely healthy subgroup (n = 414). Age groups were ranging from 1 day to 1 month, 1 – 12 months, and 1 – 5, 6 – 10, 11 – 14, and 15 – 18 years, respectively. Levels of fT3, fT4 and TSH were measured on Advia® Centaur™ automated immunoassay system.ResultsThe final sample size for reference data creation was 1,209 for TSH, 1,395 for fT3, and 1,229 for fT4. Median and 2.5/10/25/75/90/97.5 percentiles were calculated for each age group. Males had greater mean fT3 concentrations than females (p < 0.001). No sex-differences were found for TSH and fT4 between age-matched serum samples. Median concentrations of fT3, fT4 and TSH were greatest during the first month of life, followed by a continuous decline with age.ConclusionOur results corroborate those of previous studies showing that thyroid hormone levels change markedly during childhood, and that adult reference intervals are not universally applicable to children. Moreover, differences of our reference intervals compared to previous studies were observed, likely caused by different antibody characteristics of various analytical methods, different populations or undefined geographic covariates, e.g. iodine and selenium status.
Highlights
Age- and sex-specific reference intervals are an important prerequisite for interpreting thyroid hormone measurements in children
Analyses of TSH, free T3 (fT3), and free T4 (fT4) from undiluted serum samples of children and adolescents were performed on an automated immunoassay system (Advia® CentaurTM, Bayer Health Care Diagnostika, Vienna, Austria) using a direct chemiluminiscence detection system according to the manufacturer's instructions [9, 10]
TSH was analyzed in a two-site solid-phase format, whereas analysis of fT3 and fT4 was performed in a competitive assay
Summary
Age- and sex-specific reference intervals are an important prerequisite for interpreting thyroid hormone measurements in children. Measurement of free T3 (fT3) only indirectly reflects thyroid hormone production but may provide additional information, since most of fT3 is produced by intracellular conversion by the deiodinases. Despite their importance for interpreting individual results in clinical practice, pediatric reference values for thyroid function are scarce and published normative data often comprise only small numbers of patients [2,3,4,5,6,7]. Biological variables such as nutrition and lifestyle may influence thyroid function
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