Abstract
Aim: To assess thyroid function in children and adolescents from an iodine replete area with respect to age, pubertal stage and body size.
Methods: Thyrotropin (TSH), triiodothyronine (T3), total thyroxine (T4), free thyroxine (FT4) and the T4/T3 ratio, were determined in 440 schoolchildren (200 boys and 240 girls) aged 5-18yrs living in the Athens area (an iodine replete region). Body Mass Index (BMI), BMI standard deviation score (BMI-SDS) and Body Surface Area (BSA) were calculated.
Results: In girls, there was a negative correlation between age and TSH (r=-0.143, p=0.031), T3 (r=-0.337, p=0.0001), and FT4 (r=-0.365, p=0.001) levels. In boys, there was a negative correlation only between T3 levels and age (r=-0.207, p=0.005). TSH, T4 and T3 values in girls and T3 values in boys were lower at puberty compared to prepubertal stage (p<0.0005). Pubertal girls had lower TSH values than pubertal boys (p><0.02). Taking the 97th percentile value as cut-off point for TSH, subclinical hypothyroidism was found in 4.8% of boys and 4.4% of girls. BMI-SDS correlated negatively with T4/T3 ratio in boys and with FT4 in girls. Correlations between ΒSΑ and T3, T4, TSH and FT4 were statistically significant in girls.
Conclusions: We conclude that: a) the incidence of subclinical hypothyroidism in schoolchildren of an iodine replete area is approximately 5%, b) estrogens may have a suppressive effect on the pituitary-thyroid axis and c) while BMI is correlated negatively with T4/T3 ratio in boys and with FT4 in girls it appears that there is no significant correlation between the former and TSH in either gender.