An Initial Investigation of the Confidence Intervals for Thyroid Hormone Levels of the Infants Between the Age of 2-12 Weeks

Abstract

Objective To investigate reference intervals of thyroid hormone levels of infants between the age of 2-12 weeks. Methods From January 2009 to December 2012, a total of 953 infants between the age of 2-12 weeks who had clinic servers at Beijing Newborn Screening Center were recruited into this study. They were divided into three groups according to different age periods, 2-4 weeks group (n =416) , 4-8 weeks group (n=398) , and 8-12 weeks group (n=139) . Levels of the serum triiodothyronine (TT3) , thyroxine (TT4) , free triiodothyronine (FT3) , free thyroxine (FT4) and thyroid-stimulating hormone (TSH) were measured by chemiluminescence method. Median and P2.5, P25, P50, P75, P97.5 were calculated for levels of thyroid hormones. All markers were analyzed between gender, age and so on among three groups. Furthermore, the differences of thyroid hormones between infants and adults were also conducted. The study protocol was approved by the Ethical Review Board of Investigation in Beijing Obstetrics and Gynecology Hospital, Capital Medical University. Informed consent was obtained from all participates' parents. Results There had no significant difference among three groups of TSH (F=0.345, P=0.708) , and there had significant differences among three groups of FT3, FT4, TT3 and TT4 (F= 3.699, P=0.025; F=21.170, P=0.000; F=14.750, P=0.000; F=12.570, P=0.000) . There had no significant differences between boys and girls on the levels of TSH, FT3, FT4, TT3 and TT4 (t=1.860, 0.510, -0.360, 0.920, 1.370; P>0.05) . Thyroid hormone levels (TSH, FT3, TT3, TT4) of children at the age of 2-12 weeks were higher than those of adults, with significant differences (t=27.25, 46.77, 30.49, 5.59, P=0.000) . Conclusions The reference intervals of adults are not universally applicable to infants. It is important to establish the reference intervals of thyroid hormone levels of infants. Key words: Thyroid hormones; Confidence intervals; Chemiluminescent measurements; Infant