Reference intervals for serum TSH concentrations of healthy children from the Central Region of Brazil

Objective: The objective of this study was to determine the serum thyroid-stimulating hormone (TSH) concentration reference intervals (RIs) of healthy children aged 1 to 10 years of both sexes, living in the Central Region of Brazil. Subjects and methods: 1,735 children [869 (50.1%) female; 866 (49.9%) male] enrolled in the morning shift of 47 pre- and 83 public elementary schools in the municipality of Cuiaba, Mato Grosso, were studied by gathering anthropometric and social data and their medical history. A blood sample was collected from each child to determine the TSH concentration using the electrochemiluminescence method on a Cobas (R) 6000 modular analyzer (Analyzer series, Roche Diagnostics). Results: The RIs were determined using the 2.5 and 97.5 percentile and the mean +/- 2 standard deviations methods. After identifying the homoscedastic groups by age and sex, outliers higher or lower than three standard deviations were excluded. The distribution of serum TSH concentrations showed no significant age or sex differences. Based on the percentile method, TSH RI ranged from 0.93 to 5.86 mu IU/mL. Based on the mean +/- 2 standard deviations,TSH RI ranged from 0.30 to 5.29 mu IU/mL. Conclusion: The normal serumTSH concentration of the Brazilian children evaluated in this study differ from those of populations from other countries. Other regional population studies may validate the RIs found in this study and enable its safer use in pediatric clinical practice.