[Normal values for circulating thyroid hormones, T3 uptake and thyrotropin before and after TRH. Radioimmunoassay...

Measurements of T4, T3, rT3, T3U, and TSH (before and after TRH stimulation) were performed by RIA. 182 children, apparently euthyroid, age 2/12--14 years, were investigated in a cross sectional study. Free T4RIA and free T3RIA Indices and the ratio rT3/T3 and T4/T3 were calculated. Statistical analysis showed the following results: 1. Geometric mean serum concentrations of T4, T3, rT3 and TSH (basal) show no age related differences; T4 showed a not significant negative slope with age.--2. The ratio rT3/T3 and T4/T3 remains constant.--3. TRH induced TSH release (indicating the activity of the regulatory system) is unchanged from 2/12 to 14 years. Geometric means values, standard deviations and normal ranges are given.