Association of Thyroid Function With the Estimated Glomerular Filtration Rate in a Large Chinese Euthyroid Population

Background/Aims: We aimed to explore whether thyroid function within a normal range is associated with the estimated glomerular filtration rate (eGFR) and the incidence of chronic kidney disease (CKD) in a large Chinese population. Methods: We conducted a cross-sectional study that included 10,859 euthyroid individuals who underwent an annual regular health checkup in Jiangsu Province Official Hospital between August 2012 and August 2013. We measured the thyroid-stimulating hormone (TSH), free triiodothyronine (FT3) and free thyroxine (FT4) levels using a Roche modular analytics E170 and then calculated the eGFR using the Chinese modified Modification of Diet in Renal Disease (CMDRD) equation. Results: In multiple linear regression models, TSH was negatively associated with eGFR after adjusting for confounding factors (β = -0.072, P = 1.994×10 -22 ). The significance remained in both males and females. No significant association was observed between FT4 and eGFR. In the logistic regression model, we did not observe significant associations of TSH or FT3 with CKD. Participants in the highest quartile of FT4 versus the lowest quartile (reference) had an increased risk of CKD (OR = 1.763, P = 0.012). The risk of CKD was more pronounced in females with the highest quartile of FT4 (OR = 2.424, P = 0.029). Conclusion: Our findings suggest that TSH is associated with eGFR in euthyroid individuals and that higher FT4 is associated with an increased risk of CKD. More cohort studies are warranted to confirm whether the association is causal.