TSH, thyroglobulin (Tg), and the free T4 index were determined and related to chronological age in 24 normal boys (aged 7.6-17.6 yr; mean, 12.6 +/- 1.5 yr) and 20 normal girls (aged 7.8-17.0 yr; mean, 12.2 +/- 1.4 yr). There was no significant (P greater than 0.1) difference in mean serum TSH (3.06 +/- 2.07 vs. 2.97 +/- 2.07 microunits/ml) and Tg levels (25.3 +/- 10.0 vs. 28.0 +/- 14.8 ng/ml) or free T4 index (9.6 +/- 1.6 vs. 9.4 +/- 1.3 micrograms/dl) between boys and girls. Serum TSH levels correlated negatively with chronological age (rs = -0.518; r = -0.562; P less than 0.01), as did serum Tg levels (rs = -0.618; r  -0.545; P less than 0.01). On the other hand, a positive correlation was found between serum TSH and Tg levels (rs = 0.455; r = 0.421; P less than 0.01). Free T4 index levels did not correlate with chronological age, TSH levels, or Tg levels. We conclude that both serum TSH and Tg levels vary inversely with chronological age in children and adolescents. Also, a direct correlation was noted between serum TSH and Tg levels. These data as well as those from earlier studies may indicate that pituitary secretion of TSH contributes to serum levels of Tg. The decline in TSH with age may be the result of an increased response of the thyroid gland to TSH or a decline in the MCR of T4 with age.
Adolescent Aging