Early screening and risk assessment of osteoporosis are essential. Decreased secretion of estrogen in postmenopausal women leads to increased secretion of Receptor Activator of Nuclear Kappa-B Ligand (RANKL). The competitive binding of Osteoprotegerin (OPG) secreted by osteoblasts to RANKL is inhibited, and the formation and bone resorption of osteoclasts are enhanced, resulting in the decrease of bone mineral density and bone strength [16]. The proliferation of osteoblasts induced by the Wnt/β-catenin signaling pathway and the differentiation of pre-osteoblasts into osteoblasts promoted by the BMP signaling pathway are inhibited by estrogen deficiency. Estrogen deficiency can also increase the secretion of proinflammatory factors such as IL-1, IL-6 and tumor necrosis factor α (TNFα), and promote osteoclast formation [17]. Both osteocytes and osteoclasts contain insulin and IGF-1 receptors. Deficiency in bone development and maturation produces systemic IR and bone-specific IR, which in turn regulates glucose homeostasis and energy metabolism through Osteocalcin (OC) [18]. Insulin can stimulate bone formation and resorption through mitogen-activated protein kinase (MAPK) and Phosphatidylinositol 3-Kinase (PI3K) signaling pathways. Thus, it increases the growth, proliferation and survival of osteoblasts, which in turn increases bone mass. IR inhibits OC production by increasing insulin secretion and hyperinsulinism, which in turn affects BMD [19]. The TyG index, as an emerging assessment method of IR, is negatively correlated with BMD [10, 20]. A cross-sectional study in the United States showed that TyG index had a nonlinear relationship with bone mineral density, and the risk of osteoporosis increased with the increase of TyG index, and was not affected by gender and race [14]. A large Chinese population cross-sectional study showed that TyG index can effectively and objectively predict the risk of osteoporosis in women and people aged ≥ 60 and < 60 [21]. The results of our team further confirmed that TyG index had a nonlinear relationship with T-values of three different sites, and the TyG index had a better predictive effect on osteoporosis in people aged ≥ 60 and those aged ≥ 60 with abnormal FBG and/or TG. A 6-year follow-up, which used the TyG index as the best predictor of fragility fracture endpoint events in postmenopausal patients with type 2 diabetes and postmenopausal osteoporosis, found that type 2 diabetes patients with normal bone mineral density had a higher risk of fracture [22]. This prospective study lays the foundation for the TyG index to be used as an independent or auxiliary predictor in clinical research and opens up a new perspective for predicting osteoporotic fractures.
ROC analysis is a statistical method that shows the performance of classification models by drawing curves, which is widely used in clinical screening, diagnosis, and treatment [23]. The UK Health system [24] screened the prevalence of colorectal cancer (CRC) in the UK by drawing the ROC curve model of fecal hemoglobin concentration. ROC analysis used AUC as the main measure of accuracy, and sensitivity and specificity as auxiliary criteria [25]. AUC represents the area under the ROC curve, and the superiority and inferiority of the model are judged by comparing the size of the AUC. In this study, the maximum AUC of the TyG index screening was presented in postmenopausal women aged ≥ 60 with abnormal FBG and/or TG, indicating that such people have a higher risk of osteoporosis. Sensitivity represents the true positive rate, which is the rate at which actual patients are detected. The TyG index has the best sensitivity in postmenopausal women aged ≥ 60 with normal FBG and TG, and it is close to OSTA. The TyG index is similar to OSTA in the detection of osteoporosis in this population. Specificity, however, represents the false positive rate, which is the proportion of nonpatients in the negative population. The best specificity region of the TyG index was in postmenopausal women aged ≥ 60 with abnormal FBG and/or TG. In conclusion, the TyG index had the best performance in screening for osteoporosis in postmenopausal women aged ≥ 60. The maximum value of Youden's index, also known as the correct classification rate, corresponds to the best diagnostic critical value of the model, namely the Cut-off value. In this study, the TyG index cut-off value of postmenopausal women aged ≥ 60 was higher than that of postmenopausal women aged < 60, and the AUC, sensitivity, and specificity were better, indicating that the TyG index increased with age, and the risk of osteoporosis increased.
In this retrospective study, with OSTA as contrast, ROC analysis was used to comprehensively and objectively compare the efficacy of the TyG index in screening postmenopausal osteoporosis. Despite the innovative use of the TyG index for postmenopausal osteoporosis screening in this study, there are certain limitations. ① The participants in this study were all from Nanjing, Jiangsu Province, which could not represent the population characteristics of China and the world. ② To objectively compare the screening efficacy of the TyG index and OSTA, the population included in this study was postmenopausal osteoporosis. ③ Gender and finer age stratification were not included in the comparison of screening models. In the future, our research group will verify the efficacy of the TyG index in screening osteoporosis from GHD, NHANES, KNHANES and other public medical databases. At the same time, the objectivity of the TyG index will be further verified in the multi-center clinical study undertaken by our team.