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

Background: As thyroid hormones are essential for normal pubertal growth and sexual development, TSH, free T 3 (FT 3 ) and free T 4 (FT 4 ) levels undergo progressive modification during childhood and puberty. Aim: 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 normal-weight pubertal subjects. Subjects and methods: Chemiluminescent microparticle immunoassay was used to analyze TSH, FT 3 and FT 4 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 2.5 th and 97.5 th percentile. Results: We found a progressive and significant reduction in TSH, FT 3 , and FT 4 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 FT 3 or FT 4 . Conclusions: 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 FT 3 , and 13.09–20.61 pmol/l for FT 4 , and for pubertal adolescents between 0.76–4.51 mIU/l for TSH, 4.26–8.46 pmol/l for FT 3 and 10.94–19.09 pmol/l for FT 4 .