Serum thyroid hormone levels in healthy children from birth to adulthood and in short children born small for gestational age

Context: Age-appropriate reference ranges for thyroid hormones are required for detecting pediatric thyroid dysfunction. Data on thyroid hormones and peripheral thyroid metabolism in short children born small for gestational age (SGA) before and during GH treatment are lacking. Objectives: Our objectives were to obtain pediatric thyroid hormone reference ranges; to investigate thyroid hormones in short SGA children before puberty, during puberty, and during postponement of puberty by GnRH analog; and to evaluate thyroid hormones during GH treatment. Patients and Design: In 512 healthy children (225 females; 0-18 yr), free T4 (FT4), TSH, total T4, T3, rT3, and T4-binding globulin were determined. Reference ranges were calculated using the linearity, median, and skewness method. In 125 short SGA children (62 females; mean age 11.3 yr), thyroid hormones were analyzed before and after 2 yr of GH treatment and additional GnRH analog. Results: Thyroid references showed wide ranges postnatally and age-specific patterns thereafter, similar in boys and girls. Untreated short SGA children had similar FT4 and T4 levels as the reference population but significantly higher T3, rT3, and T4-binding globulin levels. During puberty and during GH treatment, FT4 and rT3 significantly decreased, whereas T3 significantly increased. Conclusion: Age-specific thyroid reference ranges are presented. Puberty and GH treatment both induce changes in peripheral thyroid metabolism, resulting in more biologically active T3 at the expense of less inactive rT3, possibly mediated by IGF-I. GH treatment induces altered peripheral thyroid metabolism but does not result in thyroid dysfunction. Copyright

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