Establishing reference interval for thyroid-stimulating hormone in children below two-year ages in Pakistani population

Introduction: Reference intervals (RIs) of thyroid-stimulating hormone (TSH) and free thyroxine (FT4) are age, assay and population specific. Currently, the age and assay-specific RIs for TSH are not available for children under two years of age. This study aimed to establish reference intervals for serum concentrations of TSH and FT4 in healthy children aged 1-24 months as per CLSI C28-A3 guidelines. Methods: This prospective cross-sectional study was conducted in children from 1 to 24 months visiting the clinical laboratory for serum vitamin D testing but without any recent illness, hospitalization, medication and history of maternal thyroid diseases from August 2018 to March 2019 were invited to participate in the study. Serum TSH and FT4 were measured on ADVIA Centaur (Siemens Diagnostics, US), using chemiluminescence immunoassay. Kolmogorov-Smirnov test assessed normality of the data and RIs based on central 95% of the population were established using the non-parametric approach. Results: After excluding one subject with confirmed congenital hypothyroidism, a total of 131 children were included in the study. The median (IQR) age of the study subjects was 12 months (11), and majority 78 (59.5%) were boys. The RIs were established using non-parametric approach as the data was not normally distributed. Reference interval for TSH was 0.73-4.94 mu IU/mL and for FT4 was 0.81-1.51 ng/dl. Conclusion: We established assay-specific RIs for serum TSH and FT4 in children aged 1-24 months in our population. The RIs were slightly lower from RIs developed on other platforms in different population.