Objective:To investigate the correlation between neutrophil/lymphocyte ratio (NLR) combined with low-density lipoprotein cholesterol/high-density lipoprotein cholesterol ratio (LDL-C/HDL-C) and severity of coronary lesions in patients with acute coronary syndrome (ACS).Methods:Patients who were diagnosed with ACS due to chest pain and received emergency coronary angiography in the First Affiliated Hospital of University of Science and Technology of China and the Affiliated Hospital of Anhui Medical University from January 2017 to June 2020 were enrolled in the final analysis. The data of gender, age, body mass index (BMI), past history, emergency blood routine indicators [neutrophil (NEU), lymphocyte (LYM), monocyte (MON), eosinophil (EOS), basophil (BAS), red blood cell (RBC), mean corpuscular volume (MCV), blood red cell distribution width (RDW), mean platelet volume (MPV), platelet volume distribution width (PDW)], blood lipid index [triglyceride (TG), total cholesterol (TC), HDL-C, LDL-C, very low-density lipoprotein cholesterol (VLDL-C)], and coronary angiography were collected. The results of coronary angiography were evaluated by the Gensini score. According to the Gensini score, the patients were divided into the control group (Gensini score = 0, 55 cases) and the study group (Gensini score > 0, 889 cases), and then the patients in the study group were divided into the low-Gensini-score group (Gensini score < 66, 419 cases) and the high-Gensini-score group (Gensini score ≥ 66, 470 cases). The differences in the general baseline data of the four groups were compared, and the correlation between the statistically significant data and the Gensini score was linearly analyzed, and then the combined diagnostic factors (NLR combined with LDL-C/HDL-C ratio) were obtained by Logistic regression analysis. The receiver operator characteristic curve (ROC curve) was used to evaluate the predictive value of NLR combined with LDL-C/HDL-C ratio in predicting the severity of coronary artery lesions in patients with ACS. Finally, multivariate linear regression analysis was used to establish the predictive model between NLR combined with LDL-C/HDL-C ratio and Gensini score.Results:A total of 944 patients were finally included. The differences in gender, age, BMI, hypertension, diabetes, smoking history, NEU, LYM, MON, EOS, RDW, TC, HDL-C, LDL-C, NLR, LDL-C/HDL-C ratio between the control group and the study group were statistically significant. The differences in BMI, hypertension, diabetes, smoking history, NEU, LYM, MON, EOS, TG, TC, HDL-C, LDL-C, NLR and LDL-C/HDL-C ratio between the low-Gensini-score group and the high-Gensini-score group were statistically significant. Linear regression analysis showed that compared with other indicators, the correlation between NLR, LDL-C/HDL-C ratio and Gensini score was stronger in the study group ( r values were 0.634 and 0.663, respectively, both P < 0.05). Binary Logistic regression analysis of the indicators related to Gensini score showed that NEU, LYM, HDL-C and LDL-C were independent risk factors for coronary stenosis in patients with ACS [odds ratio ( OR) were 0.189, 10.309, 13.993, 0.251, 95% confidence intervals (95% CI) were 0.114-0.313, 4.679-22.714, 3.402-57.559, 0.121-0.519, respectively, all P < 0.05]. ROC curve analysis showed that NLR combined with LDL-C/HDL-C ratio had higher predictive value in predicting the severity of coronary lesions in ACS patients [area under the ROC curve (AUC) was 0.952, 95% CI was 0.93-0.969], when the cutoff value was -3.152, the sensitivity was 98.20%, and the specificity was 81.60%. According to the results of multivariate linear regression analysis, the prediction model between NLR, LDL-C/HDL-C ratio and Gensini score was established, and the formula was Gensini score = -7.772+15.675×LDL-C/HDL-C ratio+8.288×NLR ( R2 = 0.862). Conclusion:There is a significant correlation between emergency NLR combined with LDL-C/HDL-C ratio and Gensini score in patients with ACS at admission, which has a certain predictive value for the severity of coronary artery stenosis in patients with ACS, and can be used as a predictor for evaluating the severity of coronary artery disease.