Thyroid Stimulating Hormone, T3 and T4 Population-based Reference Range and Children Prevalence of Thyroid Dysfunction: First Report from South of Iran

BACKGROUND & OBJECTIVE: The TSH reference range's validity affects the thyroid dysfunction diagnosis. The primary objective of this study is to determine the reference range, which is established according to age and region. METHODS: The data were collected retrospectively from people over the age of one who visited Motahari Clinic for routine health checkups between August 2017 and October 2019. TSH, T4, T3, personal drug usage, and thyroid history were collected. After excluding subjects with thyroid diseases and outliers, 1392 participants were analyzed. Hormone intervals of men and women ≥1 year old have been determined using the non-parametric method. RESULTS: The non-disease subjects' TSH, T3, and T4 reference ranges were 0.64 to 5.94 lU/mL, 0.91 to 2.47 ng/dL, and 5.53 to 12.48 g/dL, respectively. According to this range, total thyroid dysfunction prevalence in our study in children was 8.94%. There was no significant difference between TSH, T4 level, and gender in the non-disease population (P=0.46 and 0.13, respectively), but there was a statistical difference between sex and T3 (P =0.03). Our study also illustrates that for subjects under 18 years old and older, the hormones (TSH, T3, T4) concentration are statistically different (P≤0.001). CONCLUSION: We found a statistically difference between hormone values younger and older than age 18 (P=≤0.01); therefore, it is not appropriate to use the same reference range for children younger than age 18 and adults. There was male predominance in the population aged1-18 years old.