Reference values for fasting serum concentrations of thyroid-stimulating hormone and thyroid hormones in healthy Danish/North-European white children and adolescents.

Thyroid-stimulating hormone (TSH) and thyroid hormones influence the functions of many organ systems, as well as child development and growth. Several studies have reported an association between ethnicity and thyroid hormones. This study aims to explore pediatric serum concentrations of TSH, free triiodothyronine (fT3), and free thyroxine (fT4) and their relation to age and sex and subsequently to present pediatric reference intervals from healthy Danish/North-European white children. A population-based cohort in Denmark of 2411 (1435 girls) healthy school children and adolescents aged 6.0-18.9 years were included. Fasting concentrations of serum TSH, fT3, and fT4 were determined from venous blood samples using immunologic chemiluminescent assays. Age- and sex-dependent percentiles were generated using the GAMLSS function. Median values of fT3 and fT4, but not TSH, were lower in the older age group compared with the youngest age group for both sexes (all p < .05). A significant difference for fT3 was found between the sexes for all age groups (all p < .001). fT4 was negatively correlated with body mass index standard deviation scores in boys. In conclusion, serum concentrations of thyroid hormones vary during childhood and adolescence and differ with age and sex.