SERUM THYROTROPHIN, TRIIODOTHYRONINE AND THYROXINE LEVELS BY RADIOIMMUNOASSAY DURING CHILDHOOD AND ADOLESCENCE

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Abstract
Serum thyrotropin (TSH), triiodothyronine (T3) and thyroxine (T4) were measured by radioimmunoassay in 165 boys and 171 girls, clinically healthy, aged 6.1-16.0 yr with normal weight and height, grouped at 12 mo. intervals. The TSH values in boys ranged from 5.0 .+-. 0.6 to 6.1 .+-. 0.6 .mu.U[microunits]/ml without significance age differences. In girls, TSH level was 5.3 .+-. 0.5 .mu.U/ml at the ages of 6.0-7.0 and 7.4 .+-. 0.5 .mu.U/ml at the ages of 10.1-11.0 (P < 0.001). Girls had higher values than boys from 9.1-11.0 yr (P < 0.025). In boys the T3 level was 182 .+-. 10 ng/100 ml at ages 6.0-7.0 and 230 .+-. 15 ng/100 ml at ages 11.1-12.0 (P < 0.025). Girls had higher values from the age of 9.1 on (215 .+-. 12 ng/100 ml), but after 13.1 yr they decreased (P < 0.025). Girls had higher T3 levels than boys at ages 10.1-11.0 (P < 0.025), but this difference disappeared when T3 concentrations in girls of this age were compared to boys ages 11.1-12.0. In boys and girls, T4 levels tended to be lower with increasing age (r = -0.860, P < 0.01) and there was a significant difference between the values seen up to 9.0 yr and those after 13.1 yr (P < 0.025-< 0.001). Girls had lower values then boys at the ages of 8.1-9.0; however, this difference disappeared when girls of this age were compared to boys 9.1-10.0 yr old. Previous to and around puberty initiation in both sexes, there is a rise in T3, followed by a progressive decrease in T4 with a rise in TSH only in girls. These changes occurred 1 yr earlier in girls than in boys. These observations may represent transient adaptation responses to the increasing energy needs during periods of rapid growth.