The number of people in China who suffer from cardiovascular disease has been growing as a result of an aging society and a high prevalence of unhealthy lifestyles. Coronary artery disease (CAD) has become one of the diseases that seriously threaten human health [1], and caused 365,914 deaths worldwide in 2017. About two out of every 10 deaths from coronary heart disease occur in adults under 65. In developed countries, millions of patients with chest pain are typically hospitalized each year. About 50% of them were diagnosed with coronary heart disease, including stable angina pectoris, unstable angina pectoris and acute myocardial infarction [2]. That causes huge economic burden to patients and society. It is reported that at the beginning of 2010, the total hospitalization cost of cardiovascular disease patients exceeded ¥40 billion, accounting for more than 1.60% of the national health expenditure [3]. With the percutaneous coronary intervention (PCI) technology’s ongoing advancements, PCI has revolutionized the management of CAD patients [4]. However, adverse clinical outcomes continue to occur in some patients treated with PCI [5]. Current predictors for assessing the prognosis of CAD have included inflammatory marker, low density lipoprotein cholesterol (LDL-C), hypertension, diabetes, smoking, and other relevant factors affecting cardiovascular disease [6]. The clinical value of serum albumin (ALB) and other functional proteins for the prognostic assessment of CAD has been well documented [7]. Serum ALB, the main protein contained in human plasma, not only has anti-inflammatory and anti-platelet aggregation effects but also is the most significant antioxidant in whole blood [8]. Low levels of serum ALB have now become an independent predictor of many cardiovascular diseases. It has been shown that low serum ALB levels are significantly associated with the occurrence of MACE [9]. A meta-analysis [10] proved that low levels of serum ALB were associated with an increased risk of CAD. Moreover, a study by Zhu L et al. [11] found that low levels of serum ALB were a strong predictor of all-cause mortality in patients with the acute coronary syndrome (ACS). Among the globulins (GLB), immunoglobulins are their main components, which partly reflect the inflammatory condition of the body [12]. Immune inflammation plays an important role in the occurrence of atherosclerosis. The formation, growth, differentiation and rupture of atherosclerotic plaques are all affected by the immune system [13]. The globulin-to-albumin ratio (gar) is the ratio of the serum globulin level and the serum albumin level, it reflects the systemic inflammatory response and has been used to predict the poor prognosis of various cancers and chronic diseases in previous reports [14]. Studies by Takayuki Shimizu [15] have shown that GAR can predict the prognosis of patients with gastric cancer after radical resection. Hiroyuki Hachiya’s study [16] demonstrated that GAR can be used as an independent predictor of postoperative survival in patients with colon cancer. Chunjian Li’s study [17] demonstrated GAR’s predictive value for 3-month functional prognosis in patients with acute ischemic stroke. However, although GAR has been shown to have predictive value in the prognosis of tumor patients and patients with acute cerebrovascular disease, there are few studies on the relationship between GAR and the prognosis of cardiovascular disease, the relationship between GAR and post-PCI clinical outcomes for CAD patients remains unclear. In our study, we utilized data from a large prospective cohort to analyze the predictive value of GAR for adverse outcomes in post-PCI patients with CAD.

The results of the study show that a higher GAR is a significant predictive factor of adverse events in patients undergoing PCI for coronary heart disease. The optimal cut off value of GAR is 0.76, was studied by drawing ROC curve. And the patients were divided into high-value GAR groups and low-value GAR groups according to this value. The high-value groups and the low-value group were independently related to ACM, CM, MACE, and MACCE events. Kaplan–Meier survival analysis suggested that patients with high GAR group exhibited increased accumulated risk of ACM, CM, MACE and MACCE events. The results showed that GAR has an advantage over ALB and GLB in predicting all-cause mortality according to the comparison of areas under the ROC curve.

Cardiovascular disease (CVD) is the leading cause of death in the Chinese population [18]. According to the relevant reports, the prevalence of CVD in China has been still increasing steadily, and the number of CVD patients in China is currently about 330 million, while in 2019, CVD occupied first place in the composition of disease-related death among urban and rural people in China, of which the mortality rate of CAD-related death has reached 121.59/100,000 [19]. In the pathogenesis of CAD, the “theory of endothelial injury - response”, which has been recognized by most researchers, proposes that endothelial cell dysfunction can secrete inflammatory substances that promote leukocyte adherence, adhesion, aggregation, and migration to the subendothelium, thus promoting the development of atherosclerosis (AS) [20]. At the same time, the inflammatory response decreases the stability of the AS plaque leading to its rupture, thus causing ACS [21].

Currently, a variety of inflammatory biomarkers have been found to be associated with coronary heart disease and used as independent predictors to predict the long-term prognosis of patients with coronary heart disease. In recent years, a new inflammatory marker, lymphocyte to monocyte ratio, has been proven in Qian Wang’s study [22] to have a strong independent predictive value for hospitalization and long-term adverse events in patients with ST-segment elevation myocardial infarction after initial PCI. In a meta-study, the neutrophil to lymphocyte ratio (NLR) was demonstrated to be useful for assessing the risk level of patients with St-segment elevation myocardial infarction after PCI [23]. Tomasz Urbanowicz’s research [24] has proven that increased postoperative NLR, as a marker of inflammatory response, is associated with medium-term mortality in Off-pump coronary artery bypass grafting (OPCAB) patients. Therefore, inflammatory markers have important predictive value for the occurrence of adverse events in patients with coronary heart disease after PCI.

GAR is a novel inflammatory marker. We hypothesized that GAR is associated the risk of adverse clinical outcomes mainly through antioxidant and anti-inflammatory responses, and in higher GAR patients the antioxidant and anti-inflammatory response abilities are decreased, thus increasing the risk of adverse clinical outcomes. Serum ALB is synthesized in the liver, which has a variety of physiological functions, including the regulation of coagulation, anti-inflammatory, antioxidant, and maintenance of normal vascular permeability [25]. Serum ALB can bind and transport inflammatory substances and inflammatory mediators thereby regulating systemic and organ inflammatory responses and relieving oxidative stress [26]. Chronic inflammation and infection are associated with coronary heart disease and atherosclerosis. In the inflammatory state, the increased activity of macrophages and other immune system cells leads to the production of cytokines that shift protein synthesis in the liver from serum albumin to other acute phase proteins, resulting in reduced levels [27]. LDL oxidation is one of the early steps in the atherogenic process. Serum ABL inhibits the production of free hydroxyl radicals in the copper-containing ions and H${}_2$O${}_2$ system, and can scavenge peroxygen radicals, as well as inhibit the copper-dependent lipid peroxidation system [28]. A growing number of studies have shown that lower serum ALB levels are an independent risk factor for CAD. A study by Meng H et al. [29] proved that low serum ALB levels were associated with cardiovascular mortality and incidence. The Prenner SB’s study [30] showed that serum ALB is a strong prognostic factor for heart failure with lower ejection fraction. Suzuki S et al. [31] found a predictive effect of low serum ALB levels on the occurrence of MACE events in patients with stable CAD. Hong SI et al. [32] found that lower serum ALB levels were also independently associated with death caused by sudden cardiac arrest. According to Wallentin L et al. [33], higher GLB is also a risk factor for the development of cardiovascular mortality in patients with CAD. Chenglong Zhang et al. [34] demonstrated that globulin was independently correlated with Gensini score and the incidence of three-vessel lesions in patients with ACS, suggesting that globulin may be a qualified indicator for evaluating the severity of coronary artery stenosis, Cheung CL demonstrated that GLB was a predictor of all-cause mortality, cardiovascular mortality, and co-cardiovascular events in multiple groups of patients [35].

The diagnostic biomarker used in this study, the GAR, reflects the ratio between non-ALB proteins and serum ALB. Although most current studies have shown the predictive value of serum ALB for the occurrence of adverse events in patients with CAD, serum ALB concentrations are affected by physiological and pathological conditions in patients when performing laboratory tests, while these conditions have a smaller effect on the GAR. The GAR is a combined indicator of serum ALB and non-ALB proteins, whose predictive significance for CAD is not solely influenced by lower serum ALB or higher GLB. In our study, we compared the ROC curve area of the GAR, GLB, and ALB, for predicting all-cause mortality in patients with CAD, and the results showed that the GAR is more predictive than GLB and ALB alone. Therefore, compared with low serum ALB levels or high GLB levels, the predictive value of the GAR is more advantageous for the occurrence of adverse events in post-PCI patients with CAD.

First of all, this study is a single-center, observational and prospective cohort study, and GAR is a relatively new biological indicator, and its relationship with prognosis still needs to be confirmed by further large-scale studies. Secondly, details about coronary anatomy were not registered. So it is not clear whether GAR’s assessment of long-term prognosis differs among patients according to coronary heart disease severity and PCI outcome.

This study demonstrates that high GAR can be an independent predictor of adverse events in post-PCI patients with CAD. Moreover, because the ratio of serum globulin to albumin is easy to measure and relatively low in cost, GAR level at admission may be considered as part of risk stratification when PCI is possible in patients with coronary heart disease. In addition, the combination of hypertension, diabetes and other traditional risk factors helps to identify patients with coronary heart disease who are prone to death after PCI or poor prognosis such as MACE and MACCE events, and to follow up high-risk patients closely. Further studies are needed to confirm the findings of GAR in relation to adverse events after PCI in patients with coronary heart disease.

The datasets used and/or analyzed during the current study available from the corresponding author on reasonable request.

Conceived and designed the study: XX, S-FW, T-TW, Y-YZ. Data collection and analyzed the data: S-FW, T-TW, Y-YZ, X-GH, H-TY, and YY. Quality control the study and revision: XX, S-FW, T-TW, Y-YZ, X-GH, H-TY, and YY. Wrote the paper: XX, S-FW, T-TW. All authors read and approved the final manuscript. All authors have participated sufficiently in the work and agreed to be accountable for all aspects of the work.

Because all indicators were obtained from the medical record system, the informed consent exemption was applied for. The study protocol was approved by the Ethics Committee of the First Affiliated Hospital of Xinjiang Medical University (Y101310008), and the requirement for informed consent was waived by the ethics committee.

Not applicable.

This research was funded by the National Natural Science Foundation of China (82170345 and 82000238).

The authors declare no conflict of interest. Xiang Xie and Ying-Ying Zheng are serving as the Guest editors of this journal. We declare that Xiang Xie and Ying-Ying Zheng had no involvement in the peer review of this article and have no access to information regarding its peer review. Full responsibility for the editorial process for this article was delegated to Lloyd W. Klein.