We evaluated serum thyroid hormones, TSH, and prolactin before and after induction of TRH and thyroid microsomal autoantibodies in 91 diabetic children and adolescents (mean age 11.11 ±4.13 yr), with illness ranging from a few days to 14.25 yr, and in 127 “short-normal” subjects (mean age 10.32 ± 3.18 yr). All were clinically euthyroid. The control pubertal subjects showed T4, rT3, TBG, and rT3/T3 ratio values that were significantly lower than those of prepubertal subjects. The PRL area was significantly higher in pubertal than in prepubertal females. In diabetic patients, differences between pubertal and prepubertal subjects were similar to those of controls regarding T4 levels and PRL area only. T3, T4, and fT3 appeared to be significantly lower than in controls, while the rT3/T3 ratio was higher. A negative correlation (r = −0.277, P = 0.009) between T3 and HbA1 levels was demonstrated. Furthermore, thyroid function was not different in subjects with or without retinal changes or in subjects with or without residual B-cell function. Microsomal autoantibodies were observed in 6.25% of the subjects examined, though none showed any clinical or humoral sign of impaired thyroid function. In conclusion, the lower T4 and rT3 values detected in pubertal controls suggest an increased efficacy of peripheral thyroid activity in this particular life span. Considering the fact that, in diabetic children, such a decrease in rT3 at puberty is not present and that the T3 value in diabetic children is persistently lower than in controls, it would seem that even diabetic children show a “low T3 syndrome”, as in adult diabetic subjects.

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