The TyG index has been reported to be positively associated with cardiovascular risk factors [14, 18]. In addition, some studies found that the TyG index was also related to the prevalence of CVD [10, 19]. However, the prognostic value of the TyG index in patients with symptomatic CAD remains undetermined.
In this study, we investigated whether the TyG index was associated with the prevalence of atherosclerosis, which was independent of conventional cardiovascular risk factors. We confirmed the prognostic value of the TyG index in symptomatic CAD. To the best of our knowledge, there are few studies on the relationship between the TyG index and the presence of carotid and coronary atherosclerosis among patients with symptomatic CAD. Furthermore, the TyG index showed higher predictability for symptomatic CAD than did fasting triglycerides and glucose.
The TyG index was first studied as a marker of identifying insulin resistance (IR) with a high sensitivity and specificity [4, 20, 21], which has been proposed as an important cause of cardiovascular disease (CVD) . It was demonstrated that the TyG index was a useful predictor of T2DM, as well as CVD [19, 23, 24]. Moreover, studies showed that the TyG index is associated with the risk of CVD compared to the usual tool for insulin resistance evaluation . Subsequently, several studies verified the relationship between the TyG index and atherosclerosis and CAD.
To date, very few studies have examined the relationship between the TyG index and atherosclerosis. Irace et al.  evaluated the association between carotid atherosclerosis and the TyG index after adjustment for traditional cardiovascular risk factors and positive results. Whereafter, Alizargar and Bai  reported that the TyG index could predict only CCA-IMT independent of other risk factors. In a recent study, Lambrinoudaki et al.  confirmed that the TyG index is associated with carotid atherosclerosis and arterial stiffness mainly in lean postmenopausal women. In the same year, Lee et al.  showed an independent relationship between the TyG index and coronary artery stenosis in patients with type 2 diabetes. However, all these studies have limitations, such as using only postmenopausal women or patients with type 2 diabetes.
In the present study, we demonstrated that the TyG index was independently associated with the prevalence of atherosclerosis in patients with symptomatic CAD. We analyzed the carotid artery and coronary artery separately, indicating that the TyG index can predict arteriosclerosis from the peripheral vascular and central vascular aspects.
On the other hand, in recent years, there have been relatively more studies on the relationship between the TyG index and CAD [22, 30, 31]. da Silva et al.  reported that the TyG index was positively associated with CAD in the symptomatic phase, independent of social, clinical and food consumption characteristics. However, it did not compare the diagnostic values of fasting glucose and triglyceride levels with the TyG index . Whereafter, Won et al.  found that the TyG index is an independent predictor for the progression of CAC, especially in adults without heavy baseline CAD. Recently, Park et al.  reported that the TyG index is an independent marker for predicting subclinical CAD in individuals conventionally considered healthy.
On this basis, the predictive and diagnostic value of the TyG index for CAD with clinical symptoms is worth studying.
In this study, on the basis of verifying the relationship between the TyG index and cardiovascular risk factors, we compared the diagnostic efficacy of the TyG index and fasting glucose and triglycerides on symptomatic CAD. We proved that the TyG index has a better diagnostic value for symptomatic CAD. According to the formula of the TyG index, we can see that fasting glucose and triglycerides have a direct impact on the results, but this study verified that the predictive value of the TyG index for symptomatic CAD is much higher than that of the former two.
There were several limitations in the present study. First, the sample size might not be large enough, and the follow-up period might not be long enough. Second, this is a retrospective observational study that has a memory lapse, and the description of symptoms is not accurate. Third, other confounding factors, such as exercise habits and job category, were not included. Thus, we could not adjust for nutritional habits, which can affect blood glucose and triglyceride levels. Last, we verified the relationship only between the TyG index and symptomatic CAD but not subclinical CAD. Thus, it can also be seen from the bar chart that whether there is a relationship between the TyG index and patients without diabetes and hyperlipidaemia still needs to be studied.