RESUMO
This study aimed to evaluate the effects of thyroid hormone supplementation on growth rate of children with idiopathic short stature (ISS) and low-normal serum free thyroxine FT4 who were receiving growth hormone therapy. We selected 64 prepubertal children with FT4 levels in the lowest third of the normal range as the lower FT4 group, and these children were divided randomly into two subgroups: L-thyroxine (L-T4)-treated subgroup was treated with L-T4 (0.5-3.0 g/(kg·d)) from the beginning of the study, and the non-L-T4-treated subgroup received placebo. We also selected 39 ISS children with FT4 in the upper two-thirds of the normal range as the higher FT4 group. During the first year, the lower FT4 group featured lower FT3, FT4, thyroid stimulating hormone (TSH), and insulin-like growth factor-I standard deviation score (IGF-I SDS) and significantly lower height velocity (HV) compared with the higher FT4 group. However, in the lower FT4 group, the L-T4-treated subgroup presented higher FT4, FT3, TSH, and IGF-I SDS concentrations and significantly higher HV compared with children in the non-L-T4-treated subgroup. In children with ISS, the negative effect of thyroid hormone deficiency on growth rate should be considered when FT4 level lies in the low-normal range prior to recombinant human growth hormone treatment.