Reference ranges for thyroid hormones in normal Italian children and adolescents and overweight adolescents

As thyroid hormones are essential for normal pubertal growth and sexual development, TSH, free T₃ (FT₃) and free T₄ (FT₄) levels undergo progressive modification during childhood and puberty.

To establish thyroid hormone reference ranges in pre-pubertal children, pubertal adolescents, and adults and to evaluate any differences in thyroid function between overweight and normalweight pubertal subjects.

Chemiluminescent microparticle immunoassay was used to analyze TSH, FT₃ and FT₄ concentrations in serum samples from 508 children and adolescents aged 6 to 18 yr and 100 healthy adults aged 30 to 60 yr, and from 68 overweight pubertal adolescents. As data were not normally distributed, we compared them through non-parametric tests for independent samples and the reference ranges were assumed to lie between the 2.5th and 97.5th percentile.

We found a progressive and significant reduction in TSH, FT₃, and FT₄ levels in the three groups with increasing age. TSH levels were significantly higher in overweight patients than in the normal-weight group, but there were no significant differences for FT₃ or FT₄.

This study revealed significant differences in levels of thyroid hormone between different age groups and allowed us to establish normal reference ranges for pre-pubertal children between 0.87-5.19 mIU/l for TSH, 4.75-8.59 pmol/l for FT₃, and 13.09-20.61 pmol/l for FT₄, and for pubertal adolescents between 0.76- 4.51 mIU/l for TSH, 4.26-8.46 pmol/l for FT₃ and 10.94-19.09 pmol/l for FT₄.