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Pediatric reference intervals for serum thyroxine, triiodothyronine, thyrotropin, and free thyroxine.

Thyroid function tests provide information about hormone metabolism and thyroid dysfunction. Reference intervals enable clinicians to evaluate thyroid function. Several pediatric reference intervals for thyroid function tests have been published(1)(2)(3)(4). Laboratory tests and their nomenclature have been published (5), and the American Thyroid Association has classified thyrotropin (TSH) as the best single measurement of thyroid status because of its high sensitivity (6). However, reference intervals that are derived from small numbers of patients are not reliable for accurately evaluating test results that are dependent on covariates such as age and sex. The IFCC has recommended a minimum of 120 subjects for nonparametric methods in which subgrouping of data is performed (7). Virtanen et al. (8) have proposed that a smaller sample size may be sufficient for regression-based reference intervals.

Recently, there has been much interest in using hospital databases to extract large volumes of patient data for clinical research(9)(10)(11)(12). Hospital databases provide a sufficient number of subjects for evaluating age and sex differences and for establishing age- and sex-based reference intervals. Test results can be affected by medications or treatment received by patients for thyroid disease that alter the physiologic features of the thyroid hormone concentrations during the neonatal period (13)(14). Therefore, neonates and patients who have thyroid disease or demonstrate abnormal test results should be excluded from the analysis used to establish the reference intervals.

Here we report health-related reference intervals for serum thyroxine (T4), triiodothyronine (T3), TSH, and free T4 to be used as clinical guidelines for screening patients with suspected thyroid dysfunction. These pediatric norms are more accurate than those previously published because they are age- and sex-specific and were derived from a large population of children and …