[Establishing reference intervals of thyroid hormone based on a laboratory information system]

Objective: To establish reference intervals (RIs) of thyroid hormone based on data from healthy subjects in laboratory information system (LIS) by indirect methods. Methods: Data were selected from the physical examination center in LIS of the First Hospital of Jilin University from May 2014 to December 2018. The normal distribution of the original data was checked by the Kolmogorov-Smirnov test. Skewed data were transformed into normal distribution using BOX-COX techniques, and outliers were identified by the Turkey method. The continuous percentile curve was established by coefficient of skewness-median-coefficient of variation(LMS) methods. Cut-off value of age was determined by decision trees, and the differences between groups were verified by Z-tests. P(2.5) and P(97.5) in the RIs were analyzed by non-parametric methods. Results: A total of 45 742 subjects were included in the study. There were no differences in the RI for thyroid stimulating hormone (TSH) among age groups or between men and women (Z*), and the RI was 0.60-4.41mIU/L (20-79 years old). However, the levels of free triiodothyronine(FT(3)) decreased with age in males and females under 35-year-old. The RIs for FT(3) were 4.47-6.44pmol/L (20-44 years old), 4.19-6.21pmol/L (45-64 years old) and 3.90-5.85pmol/L (65-79 years old) in males, and 4.04-6.13pmol/L (20-34 years old) and 3.87-5.76pmol/L (35-79 years old) in females, respectively. The levels of free thyroxine(FT(4)) in men were higher than those in women from 20 to 49 years old, and no gender and age differences could be viewed in subjects after 50 years old (Z*). The RIs for FT(4) were 13.69-21.76pmol/L (male, 20-49 years old), 12.99-20.83pmol/L (female, 20-49 years old) and 12.98-21.21pmol/L (50~79 years old). Conclusion: Establishment of RIs of thyroid hormone based on the data from LIS is simple and reliable, which is suitable for clinical laboratory application.