Serum triiodothyronine concentrations in infancy, childhood, adolescence and pediatric thyroid disorders

Measurements of serum total triiodothyronine (T₃) concentrations were performed in infants, children, and in adolescent subjects from 3 days to 18 years of age, and in pediatric patients with hypothyroidism and hyperthyroidism. Mean serum T₃ concentrations were 140 ± 16.2 ng/100 ml (mean ± 1 SE of the mean) in 3-day-old infants and 124 ± 8.3 ng/100 ml in 1-2-yr-old infants. Mean T₃ levels in children were 138 db 2.6 ng/100 ml at ages 3-4 yr, 142 ± 4.7 ng/100 ml at 5-7 yr, and 132 ± 4.4 ng/100 ml at 8-10 yr. In adolescence, mean serum T3 concentrations were 129 ± 4.6 ng/100 ml at 11- 13 yr and 134 db 5.9 ng/100 ml at 14-18 yr. No significant differences in serum T₃ concentrations were found with puberty, and male and female children and adolescents had similar T₃ levels. Patients with hyperthyroidism had serum T₃ concentrations from 240-1200 ng/100 ml while hypothyroid subjects had serum T3 concentrations from 66-82 ng/100 ml.