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

Abstract

ABSTRACT Serum thyrotrophin (TSH), triiodothyronine (T 3 ) and thyroxine (T 4 ) were measured by radioimmunoassay in 165 boys and 171 girls, clinically healthy, aged 6.1 to 16.0 years with normal weight and height, grouped at 12 months' intervals. The TSH values in boys ranged from 5.0 ± 0.6 to 6.1 ± 0.6 μU/ml without significant age differences. In girls, TSH level was 5.3 ± 0.5 μU/ml at the age of 6.0 to 7.0 and 7.4 ± 0.5 μU/ml at the age of 10.1 to 11.0 ( P < 0.001). Girls had higher values than boys from 9.1 to 11.0 years ( P < 0.025). In boys the T 3 level was 182 ± 10 ng/100 ml at age 6.0 to 7.0 and 230 ± 15 ng/100 ml at age 11.1 to 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 years they decreased ( P < 0.025). Girls had higher T 3 levels than boys at age 10.1 to 11.0 ( P < 0.025), but this difference disappeared when T 3 concentrations in girls of this age were compared to boys aged 11.1 to 12.0. In boys and girls, T 4 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 years and those after 13.1 years ( P < 0.025 − < 0.001). Girls had lower values than boys at the age of 8.1 to 9.0; however, this difference disappeared when girls of this age were compared to boys 9.1 to 10.0 years old. It is concluded that previous to and around puberty initiation in both sexes, there is a rise in T 3 , followed by a progressive decrease in T 4 with a rise in TSH only in girls. These changes occurred one year earlier in girls than in boys. These observations may represent transient adaptation responses to the increasing energy needs during periods of rapid growth.