Clin Chem. 1996;. Ridgway EC. Modern concepts of primary thyroid gland failure. Clin Chem. 1996;. Nicoloff JT, Spencer CA. The use and misuse of the sensitive thyrotropin assays. J Clin Endocrinol Metab.
Two-tailed values of P 0.05 were considered statistically significant. SAS, Ver. 6.12 (SAS Institute and SPSS, Ver. 8.0 (SPSS were used for statistical analysis. Table 1 presents the pediatric reference intervals, the mean thyroid hormone concentrations, and the number of children analyzed for each age group and sex.
Infants less than 1 month of age and premature infants were also excluded from analysis. Results from patients who had multiple measurements on the same thyroid function test ( 8 for each analyte) were averaged to obtain a single value for each patient in the study.
Because of the extreme right-tailed skew of the TSH and free T4 distributions, natural log transformations were applied before analysis ( 22 ). Analysis of covariance was used to compare slopes and y -intercepts between females and males.
Euthyroid mean values for T4 were estimated to be higher for females than males in the same age group ( P 0.0001). Earlier studies( 1 24 ) found a similar inverse relationship between T4 and age; however, no sex differences were reported.
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Clin Chem. 1996;. Uy HL, Reasner CA, Samuels MH. Pattern of recovery of the hypothalamic-pituitary-thyroid axis following radioactive iodine therapy in patients with Graves disease. Am J Med. 1995;. Davis JRE, Black EG, Sheppard MC.
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1998;. Lamberg BA, Helenius T, Liewendahl K. Assessment of thyroxine suppression in thyroid carcinoma patients with a sensitive immunoradiometric TSH assay. Clin Endocrinol. 1986;. Braverman LE. Evaluation of thyroid status in patients with thyrotoxicosis.
Our reference intervals for free T4 are broader than those reported by others ( 4 ). Acquisition of clinical data to establish pediatric reference intervals for thyroid function testing is challenging because of the difficulty in obtaining blood samples from a large number of healthy children.
Nelson JC, Clark SJ, Borut DL, et al. Age related changes in serum free thyroxine during childhood and adolescence. J Pediatr. 1993;. Fisher DA. Physiological variations in thyroid hormones; physiological and pathophysiological considerations.
Therefore, the number of tests used to define pediatric norms is limited. Hospital databases contain large stores of clinical data that can be used to establish reference intervals if the appropriate selection criteria are applied( 9 10 26 ).