Abstract: Background　Previous studies have demonstrated an inverse association between subclinical hypothyroidism and osteoporosis (OP) risk in postmenopausal women. However, the precise effects of subclinical hypothyroidism on bone mineral density and its specific sites of action remain inconclusive. Objective　To study the relationship between thyroid function indicators and bone mineral density at different sites in premenopausal and postmenopausal patients with subclinical hypothyroidism, and to explore predictive factors for osteoporosis. Methods　A retrospective study was conducted on 591 women aged 40-60 years with subclinical hypothyroidism who underwent physical examinations at the Health Management Center of Guizhou Medical University Affiliated Hospital between 2023 and 2024. Participants were categorized by menopausal status into premenopausal women (n=189) and postmenopausal women (n=402). Serum levels of free triiodothyronine (FT3), free thyroxine (FT4), thyroid-stimulating hormone (TSH), aspartate aminotransferase (AST), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C). Bone mineral density (BMD) was measured at the lumbar spine, femoral neck and total hip in both groups. Pearson correlation analysis and multiple linear regression analysis were employed to investigate the correlation between thyroid indicators and bone density at various sites. Receiver operating characteristic (ROC) curves were plotted to explore the predictive value of FT3 for osteoporosis in postmenopausal women. Results　Pearson correlation analysis revealed that FT3, FT4, AST and age were negatively correlated with lumbar spine bone mineral density (P<0.05); Age, FT4, AST, TC and LDL-C were negatively correlated with femoral neck bone mineral density (P<0.05); Age, FT4 and HDL-C were negatively correlated with total hip bone mineral density (P<0.05); Height, body weight and BMI were positively correlated with lumbar spine, femoral neck and total hip bone mineral density (P<0.05). Multivariate linear regression analysis revealed that FT3 ( β=-0.120, P<0.05), body weight (β=0.267, P<0.05), and age (β=-0.401, P<0.05) were significant predictors of lumbar spine bone density in female examinees overall; FT3 (β=-0.161, P<0.05), body mass (β=0.201, P<0.05), and age (β=-0.235, P<0.05) were factors influencing lumbar spine bone density in postmenopausal women; FT3 was not associated with femoral neck or total hip bone mineral density in premenopausal women, postmenopausal women, or the overall female cohort (P>0.05); FT4 was not associated with bone mineral density at any site in premenopausal women, postmenopausal women, or the overall female cohort (P>0.05). ROC curve analysis revealed that FT3 predicted lumbar osteoporosis in postmenopausal women with an area under the curve (AUC) of 0.609 (95%CI=0.523-0.696), sensitivity of 69.2%, specificity of 51.0%, and optimal cutoff value of 4.605 pmol/L. Conclusion　FT3 is a significant factor influencing lumbar spine bone mineral density in postmenopausal women with subclinical hypothyroidism. A level of 4.605 pmol/L represents the optimal cutoff value for FT3 in predicting lumbar osteoporosis in this population, providing a reference indicator for preliminary screening of lumbar OP risk.

Key words: Subclinical hypothyroidism, Premenopausal, Postmenopausal, Osteoporosis, Bone density, FT3

摘要： 背景　既往研究表明绝经后妇女亚临床甲状腺功能减退症与骨质疏松症（OP）风险呈负相关，但亚临床甲状腺功能减退症对骨密度的影响及作用部位尚未形成明确结论。目的　研究绝经前及绝经后亚临床甲状腺功能减退症患者甲状腺功能指标与不同部位骨密度的关系，探讨OP的预测因子。方法　回顾性选取2023—2024年于贵州医科大学附属医院健康管理中心进行体检的591例40~60岁亚临床甲状腺功能减退症女性为研究对象，按绝经状态将其划分为绝经前女性（n=189）和绝经后女性（n=402）。检测记录受试者血清游离三碘甲状腺原氨酸（FT3）、游离甲状腺素（FT4）、促甲状腺激素（TSH）、天冬氨酸氨基转移酶（AST）、总胆固醇（TC）、低密度脂蛋白胆固醇（LDL-C）、高密度脂蛋白胆固醇（HDL-C）等生化指标，测量两组受试者腰椎、股骨颈和全髋骨密度。采用Pearson相关分析和多元线性回归分析探究甲状腺指标与各部位骨密度的相关性；绘制受试者工作特征（ROC）曲线，探究FT3在绝经后女性骨质疏松预测中的应用价值。结果　Pearson相关分析结果表明，FT3、FT4、AST及年龄与腰椎骨密度呈负相关（P<0.05）；年龄、FT4、AST、TC、LDL-C与股骨颈骨密度呈负相关（P<0.05）；年龄、FT4、HDL-C与全髋骨密度呈负相关（P<0.05）；身高、体质量、BMI与腰椎、股骨颈、全髋骨密度呈正相关（P<0.05）。多元线性回归分析结果显示，FT3（β=-0.120，P<0.05）、体质量（β=0.267，P<0.05）、年龄（β=-0.401，P<0.05）是总体检女性腰椎骨密度的影响因素；FT3（β=-0.161，P<0.05）、体质量（β=0.201，P<0.05）、年龄（β=-0.235，P<0.05）是绝经后女性腰椎骨密度的影响因素；FT3与绝经前女性、绝经后女性及总体检女性股骨颈和全髋骨密度无关（P>0.05）；FT4与绝经前女性、绝经后女性及总体检女性各部位骨密度无关（P>0.05）。ROC曲线分析结果表明，FT3预测绝经后SCH女性腰椎OP的ROC曲线下面积为0.609（95%CI=0.523~0.696），灵敏度为69.2%，特异度为51.0%，最佳截断值为4.605 pmol/L。结论　FT3是绝经后亚临床甲状腺功能减退症患者腰椎骨密度的影响因素，4.605 pmol/L是FT3预测绝经后亚临床甲减患者腰椎OP的最佳截断值，为该人群腰椎OP风险的初步筛查提供了参考指标。

关键词: 亚临床甲状腺功能减退, 绝经前, 绝经后期, 骨质疏松, 骨密度, FT3