Reference Intervals for Serum Thyroid-Stimulating Hormone Based on a Recent Nationwide Cross-Sectional Study and Meta-Analysis

OBJECTIVE: The aim of our study was to compare the reference intervals (RIs) [median (2.5(th)-97.5(th) percentiles)] for thyroid-stimulating hormone (TSH) between subgroups stratified by ethnicity and iodine status in a global context. DESIGN AND METHODS: Primary data were derived from a recently published cross-sectional study in mainland China. Secondary data were obtained from online databases. The RIs for TSH were calculated in the reference population according to the National Academy of Clinical Biochemistry (NACB) standard and in the disease-free population. A meta-analysis of ethnicity- and iodine status-specific TSH RIs was performed. RESULTS: The primary data showed that the TSH RI (mU/L) in the disease-free population was 2.33 (0.67, 7.87), which is wider than the published RI [2.28 (0.74, 7.04)] in the reference population. The meta-analysis showed that whether in the reference or disease-free population, the RIs in Yellows were much higher than those in Caucasians. In the reference population, the median and 2.5(th) percentile in the iodine-sufficient subgroup were both lower than the iodine-deficient or more-than-adequate subgroup, while the 97.5(th) percentile showed a positive trend with increasing sufficiency of iodine. However, in the disease-free population, the iodine-sufficient subgroup had a lower median and 97.5(th) percentile but higher 2.5(th) percentile than the iodine-deficient subgroup. CONCLUSION: Yellows have a higher TSH RI than Caucasians. In the reference population, both the median and 2.5(th) percentile TSH in the iodine-sufficient population were the lowest among the different iodine status subgroups, while the 97.5(th) percentile of TSH showed an upward trend with increasing iodine sufficiency.