Reference Range and Sociodemographic Characteristics of TSH among Reproductive Age Women in Rural China

Appropriate reference range of thyroid-stimulating hormone (TSH) is important to interpreting the results of thyroid functional tests. However, the reference range and sociodemographic characteristics of TSH based on large-scale studies are yet to be declared in rural China. To clarify reference range and sociodemographic characteristics of TSH in reproductive age of women from rural China. A nationwide population-based study was conducted as The National Free Preconception Health Examination Project (NFPHEP). Nearly 400,000 (n = 392,659) of Chinese rural women aged 15-55 years were randomly recruited. Predetermined strict exclusion criteria made a number of 359,895 as the reference population. Serum TSH was evaluated with enzyme-linked immunosorbent assay (ELISA). The reference range of TSH on overall and reference population was 0.39-5.20 and 0.39-5.13 uIU/ml (2.5th-97.5th percentiles), respectively. In the reference population, the range (2.5th to 97.5th percentile) of serum TSH in different age groups was 0.40-5.03 uIU/ml, 0.39-5.15 uIU/ml, 0.37-6.10 uIU/ml, and 0.44-7.03 uIU/ml, respectively. The mean TSH value in women aged 26-35 years was 2.26 uIU/ml, significantly lower than those aged 36-45 (p < 0.001). The mean TSH values for eastern, central, and western regions were 2.28 uIU/ml, 2.29 uIU/ml, and 2.24 uIU/ml respectively. The mean of serum TSH concentration was significantly higher in central region than that in western region (p ≤ 0.001). The TSH value 0.39-5.13 uIU/ml (2.5th-97.5th percentiles) was derived as a reference range of reproductive age women from rural China. We use the TSH ranges from reference population to diagnose hyperthyrotropinemia or hypothyroidism in different areas in China. The reference ranges for eastern, central, and western regions were 0.33-5.61 uIU/ml, 0.40-5.04 uIU/ml, and 0.40-4.98 uIU/ml (2.5th-97.5th percentiles) respectively. The value of serum TSH was associated with age, living region, smoking, drinking, educational level, and interpersonal tension, as well as life and economic pressure, but irrelevant to ethnicity or occupation.