Medical Service Corps of 2nd Armored Brigade, Republic of Korea Army, Paju, Republic of Korea.
Department of Internal Medicine, Nowon Eulji Medical Center, Eulji University, Seoul, Republic of Korea.
Kidney Blood Press Res. 2020;45(3):442-454. doi: 10.1159/000507290. Epub 2020 May 5.
Thyroid function is evaluated by thyroid stimulating hormone (TSH) and free thyroxine (fT4). Although many studies have indicated an intimate relationship between thyroid hormones and kidney functions, reports about the simultaneous evaluation of TSH and fT4 are rare.
We aimed to analyze the association between TSH and kidney function, with emphasis on a potential nonlinear relationship, and identify an independent relationship between fT4 and kidney function.
We reviewed the data of 7,061 subjects in the Korea National Health and Nutrition Examination Surveys who were randomly subsampled for thyroid function evaluation between 2013 and 2015. A total of 5,578 subjects were included in the final analysis, after excluding people <18 years old, and those with a short fasting time, abnormal fT4 levels, and thyroid disease or related medications. Creatinine-based estimated glomerular filtration rate (eGFR) was used to define kidney function.
A 1 mmol/L increase of logarithmic TSH was associated with decreased eGFR (β: -1.8; 95% CI -2.3 to -1.2; p < 0.001), according to multivariate linear regression analysis. On the multivariate generalized additive model plot, TSH demonstrated an L-shaped relationship with eGFR, showing a steeper slope for 0-4 mIU/L of TSH. A 1 µg/dL increase of fT4 was also associated with decreased eGFR (β: -7.0; 95% CI -0.94 to -4.7; p < 0.001) on the multivariate linear regression analysis; this association was reversed after adjusting for age. On the mediation analysis, the indirect effect via age and direct effect per 1 µg/dL increase of fT4 on eGFR was 9.9 (8.1 to 11.7, p < 0.001) and -7.1 (-9.3 to -4.8, p < 0.001), respectively.
Increased TSH was associated with decreased eGFR, particularly in the reference range. The direct effect of increased fT4 was decreased eGFR, which may be affected indirectly by age.
甲状腺功能通过促甲状腺激素（TSH）和游离甲状腺素（fT4）进行评估。尽管许多研究表明甲状腺激素与肾脏功能之间存在密切关系，但关于 TSH 和 fT4 的同时评估的报告却很少。
我们旨在分析 TSH 与肾功能之间的关联，重点是潜在的非线性关系，并确定 fT4 与肾功能之间的独立关系。
我们回顾了 2013 年至 2015 年期间随机抽取进行甲状腺功能评估的韩国国家健康和营养检查调查 7061 名受试者的数据。共有 5578 名受试者纳入最终分析，排除了<18 岁的人群，以及空腹时间短、fT4 水平异常、甲状腺疾病或相关药物治疗的人群。基于肌酐的估计肾小球滤过率（eGFR）用于定义肾功能。
根据多元线性回归分析，TSH 每增加 1mmol/L，eGFR 降低（β：-1.8；95%CI -2.3 至 -1.2；p<0.001）。在多元广义加性模型图上，TSH 与 eGFR 呈 L 形关系，TSH 在 0-4mIU/L 范围内斜率较陡。fT4 每增加 1μg/dL，eGFR 也降低（β：-7.0；95%CI -0.94 至 -4.7；p<0.001）；在调整年龄后，这种关联发生了逆转。在中介分析中，fT4 每增加 1μg/dL 对 eGFR 的年龄间接影响和直接影响分别为 9.9（8.1 至 11.7，p<0.001）和-7.1（-9.3 至 -4.8，p<0.001）。
TSH 升高与 eGFR 降低有关，特别是在参考范围内。fT4 升高的直接作用是降低 eGFR，这可能间接受年龄的影响。
