Reference Interval of Serum Thyroid Hormone in Obese Thais

Piyarat Lerttrakul, Thaval Rerkngarm, Narisa Kengtrong Bordeerat


The aim of this study was to evaluate the reference intervals of TSH, FT3, and FT4 in obese Thais. The cross-sectional study consisted of 400 subjects who were recruited after undergoing routine health check-ups at the Police General Hospital. The subjects, age 18-50 years with BMI ≥ 25 kg/m2, were divided into three sub-groups: 18-30 years, 31-40 years and 41-50 years. The results showed that thyroid hormone (FT3 and FT4) levels were higher in males than in females. TSH levels in obese, 41-50 years age group were significantly higher than those in the younger age groups. However, no statistical significance of TSH was shown between males and females. The reference intervals (p2.5-97.5) for TSH, FT3 and FT4 were 0.31-5.93 mIU/L, 0.93-1.73 pg/mL and 0.20-0.39 ng/dL, respectively. In conclusion, obesity may impact the range of normality of TSH. The reference intervals for thyroid hormones are needed to be determined for each specific population. Slightly elevated TSH concentrations in the obese could be considered acceptable, with no need for thyroxine treatment.

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