Age- and sex-specific reference intervals for thyroid hormones in a Chinese pediatrics: a prospective observational study of 1,279 healthy children

BACKGROUND: Thyroid hormones are essential for early neurocognitive development and growth and development in childhood and adolescence. However, the reference intervals (RIs) for thyroid hormones in Chinese pediatric individuals remain unclear. This study aimed to establish thyroid hormone RIs for a Chinese pediatric population according to appropriate age- and sex-specific partitioning. METHODS: In this prospective observational study, a total of 1,279 healthy children (singletons, aged from 1 day to 12 years) were recruited, and serum samples were analyzed on a Mindray automated chemiluminescence immunoassay analyzer CL-6000i for thyroid hormone detection, including thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4), total triiodothyronine (T3), and total thyroxine (T4). Age and sex-specific RIs were established, and the corresponding 95% confidence intervals (CIs) were calculated in accordance with the Clinical Laboratory Standards Institute (CLSI) document C28-A3 guidelines. RESULTS: Quantile testing revealed that the median (P50) and RIs [2.5(th) percentile (P2.5)–97.5(th) percentile (P97.5)] for TSH, FT3, T3, and T4 of males differed significantly from those of females (P<0.05), except for FT4 (P=0.483). For FT3 and T3, the RIs of males were higher than that of females, and the RI of T4 for males was narrower and higher than that of females [P2.5–P97.5: 72.33–171.60 vs. 72.31–176.27 nmol/L; P50: 116.75 vs. 113.47 nmol/L, P=0.011]. RIs for TSH, FT3, FT4, T3, and T4 showed sex- and age-specific properties and displayed a wide variation during the first month of life but gradually narrowed and concentrated with increasing age. In addition, RIs of TSH, FT3, FT4, and T3 in males differed significantly from females in the first month of life (TSH: 1.46–10.87 vs. 1.08–11.35 mIU/L; FT3: 2.96–7.08 vs. 2.35–7.27 pmol/L, FT4: 13.34–28.65 vs. 13.82–31.83 pmol/L; T3: 0.83–2.33 vs. 0.72–2.46 nmol/L). The RI of T4 also exhibited a difference between males and females in the 9- to 12-year age group (59.31–150.72 vs. 63.29–146.94 pmol/L for males and females, respectively). CONCLUSIONS: Pediatric RIs of thyroid hormones display age- and sex-specific trends. The RIs established in this study will improve the accuracy of TSH assay result interpretations and clinical decision-making in clinical laboratories that utilize the Mindray analytical platform.