Establishment of reference ranges for thyrotropin, triiodothyronine, thyroxine and free thyroxine in neonates, infants, children and adolescents.

Thyrotropin, triiodothyronine, thyroxine and free thyroxine were determined in the sera of 714 euthyreotic neonates, infants, children and adolescents (age range 5 days to 18 years), using the IMx from Abbott Laboratories. Thyrotropin, triiodothyronine and free thyroxine were determined with microparticle enzyme immunoassays (MEIA). Thyroxine was determined with a fluorescence polarization immunoassay (FPIA). The proband collective was divided into 9 age groups, and each age group into males and females. In accordance with the recommendations of the International Federation of Clinical Chemistry, the 95% scatter range was taken as the reference range. In the different age groups, the ranges of some hormones showed significant differences between males and females. When no significant difference existed between the sexes, the results for males and females were evaluated statistically as a single group. Only a few reference groups showed normal Gaussian distributions. Therefore, in addition to the 50th percentile, the 2.5th and 97.5th percentiles were also calculated for all reference groups. Minimal and maximal values were also determined. The U-test of Mann & Whitney was used to test for significant differences between individual reference groups, and groups showing no significant differences were combined. The corresponding references ranges were then calculated.