Pediatric Reference Intervals for Thyrotropin, Free Triiodothyronine, and Free Thyroxine and the Relevance of Body Mass Index and Puberty in Measurement Interpretation.

Background: The present study aimed to establish age- and sex-specific reference intervals for serum concentrations of thyrotropin (TSH), free triiodothyronine (fT3), and free thyroxine (fT4) in healthy children and adolescents. Additionally, we investigated the association of TSH, fT3, and fT4 with putative influencing factors, such as sex, body mass index (BMI), and puberty. Methods: A total of 9404 blood serum samples from 3140 children and adolescents without thyroid affecting diseases were included in determining TSH, fT3, and fT4 levels and age- and sex-specific reference ranges. To investigate the association of TSH, fT3, and fT4 with age, sex, weight status, and the role of puberty-based changes, the hormone levels and BMI values were converted to standard deviation scores (SDS). Results: In general, TSH, fT3, and fT4 were found to be age- and sex-dependent. Puberty was accompanied by decreased TSH, decreased fT3 with a temporary peak in males, and a temporary nadir of fT4 in Tanner stage 3 for both sexes. BMI-SDS was positively associated with TSH-SDS (ß = 0.081, p < 0.001); the effect was more pronounced in overweight subjects (ß = 0.142, p < 0.01) and insignificantly negative in underweight subjects (ß = -0.047, p > 0.05). BMI-SDS was positively associated with fT3-SDS (ß = 0.066, p < 0.001) and negatively associated with fT4-SDS (ß = -0.135, p < 0.001), with the effect insignificantly less negative in overweight children (ß = -0.055, p > 0.05). Conclusions: Age- and sex-specific reference intervals are important for the interpretation of measurements of TSH, fT3, and fT4 in children and adolescents. Influencing factors such as BMI and puberty should be taken into consideration when using measurements of TSH and thyroid hormones in the diagnosis, treatment, and monitoring of thyroid diseases. Clinical Trial Registration number: NCT02550236.

Socioeconomic Status Is Related to Pubertal Development in a German Cohort.

INTRODUCTION: Current health literature suggests that there has been a decline in the age of pubertal onset and that pubertal onset/duration of puberty may, besides weight status, be influenced by socioeconomic context. OBJECTIVE: The goal of this study was to determine whether pubertal onset/duration and puberty-triggering hormones luteinizing hormone (LH) and follicle-stimulating hormone (FSH) vary according to socioeconomic status (SES). Moreover, we aimed to propose cutoff values of serum LH and FSH for predicting gonadarche in boys. METHODS: 2,657 apparently healthy children and adolescents between 5.5 and 18 years from the area of Leipzig were recruited from the LIFE Child study. Age at pubertal onset/end of puberty was given in 738/573 children, respectively. Anthropometric parameters of puberty, blood measurements of LH and FSH, and questionnaires assessing SES were evaluated. RESULTS: Lower SES was associated with earlier thelarche and longer duration of puberty in overweight/obese girls, whereas age of menarche was not affected. In boys with low SES, a trend versus earlier puberty onset can be seen. Lower SES was significantly associated with boys' age at mutation. No significant differences in boys' and girls' serum levels of LH and FSH during puberty according to SES were observed. Serum LH levels of 0.56 IU/L and serum FSH levels of 1.74 IU/L showed the best prediction of gonadarche in boys. CONCLUSION: Puberty onset/duration and boys' age at mutation is affected by SES. The proposed cutoff levels for serum LH and FSH could provide a serological tool to determine gonadarche in boys.