Background. The systemic immune-inflammation index (SII) is used as an indicator of prognosis for a wide range of diseases. Thyroid function has been found to be strongly associated with inflammation. The purpose of this investigation was to analyze the correlation between SII and various thyroid functions. Methods. This study utilized data from the National Health and Nutrition Examination Survey (NHANES) 2007–2012. The association between SII and thyroid function was analyzed using weighted univariate and multivariate linear regression analyses. Subgroup analyses, interaction tests, and weighted restricted cubic spline (RCS) regression analyses were also employed to test this correlation. Results. Of the 6,875 participants (age ≥ 20 years), the mean age was 46.87 ± 0.40 years. The adjusted model showed that lnSII was negatively correlated with FT3 (β = −0.0559, 95% CI −0.1060 to −0.0059,) and FT3/FT4 (β = −0.0920, 95% CI −0.1667 to −0.0173,). There was a positive correlation between lnSII and TT4 (β = 0.1499, 95% CI 0.0722–0.2276,). In subgroup analyses, lnSII still independently affected a wide range of thyroid functions. Weighted RCS analysis showed a nonlinear relationship between FT3 and lnSII. Conclusion. Close relationships exist between SII and a variety of thyroid functions. SII can be used as an indicator to predict thyroid dysfunction. Control of inflammatory activity may be a protective measure against thyroid dysfunction. More large-scale prospective studies are necessary to further explore the correlation between SII and thyroid function and the role of obesity in this.

中文翻译：

---

美国成人全身免疫炎症指数与甲状腺功能之间的关联

背景。全身免疫炎症指数（SII）被用作多种疾病的预后指标。已发现甲状腺功能与炎症密切相关。本次调查的目的是分析SII与各种甲状腺功能之间的相关性。方法。本研究利用了 2007-2012 年国家健康和营养检查调查 (NHANES) 的数据。使用加权单变量和多变量线性回归分析来分析 SII 和甲状腺功能之间的关联。还采用亚组分析、交互作用检验和加权限制三次样条 (RCS) 回归分析来检验这种相关性。结果。在 6,875 名参与者（年龄 ≥ 20 岁）中，平均年龄为 46.87 ± 0.40 岁。调整后的模型显示，lnSII 与 FT3（ β  = -0.0559，95% CI -0.1060 至 -0.0059，）和 FT3/FT4（β  = -0.0920，95% CI -0.1667 至 -0.0173，）呈负相关。lnSII 和 TT4 之间呈正相关（β  = 0.1499，95% CI 0.0722–0.2276）。在亚组分析中，lnSII 仍然独立影响广泛的甲状腺功能。加权 RCS 分析显示 FT3 和 lnSII 之间存在非线性关系。结论。SII 与多种甲状腺功能之间存在密切关系。SII可作为预测甲状腺功能障碍的指标。控制炎症活动可能是预防甲状腺功能障碍的保护措施。需要更大规模的前瞻性研究来进一步探讨 SII 与甲状腺功能之间的相关性以及肥胖在其中的作用。