Establishment of Serum TSH Reference Intervals by an Indirect Method for Healthy Population in Southwest China

Serum thyroid stimulating hormone (TSH) detection is of great clinical significance in monitoring thyroid function. The aim of the present study was to establish reference intervals (RIs) for serum TSH in healthy Han population in Southwest China using data from routine health check-up individuals.

Healthy subjects (n = 7,116) were enrolled from January 2019 to September 2020. Serum TSH values were determined in the Beckman Coulter UniCel™ DxI 800 Access® immunoassay system. Outliers were identified and removed using Dixon's interactive principle. The 95th percentile range was calculated as RIs for serum TSH. All the statistical analyses were run on R statistical software version 4.0.3.

A total of 6,668 (1,324 female and 5,344 male) suitable individuals were included in this study. Serum TSH results showed a non-Gaussian distribution by Kolmogorov-Smirnov test. According to Mann-Whitney U analysis, the serum TSH values for the female group differ from the male group's (p < 0.05). Besides, Spearman's rank correlation test disclosed that no obvious correlation was observed between serum TSH levels and age (r = -0.0039, p > 0.05). Accordingly, the RIs for serum TSH in Southwest China Han population were 0.64 (95% CI: 0.62 to 0.65) to 4.05 (95% CI: 4.02 to 4.09) mIU/L in male and 0.72 (95% CI: 0.67 to 0.77) to 5.66 (95% CI: 5.58 to 5.75) mIU/L in female, respectively.

In this study, the laboratory specific RIs for serum TSH were successfully established by indirect method using the data from health check-up population. It implies that the indirect method is an easy and lowcost pathway for each laboratory to establish its own RIs.