Objective:To investigate the relationship between antithrombin Ⅲ (AT-Ⅲ) levels and CHA2DS2-VASc scores to assess the thromboembolism risk in patients with non-valvular atrial fibrillation (NVAF), and to explore the value of AT-Ⅲ in the risk assessment of thrombosis in these patients.Methods:We enrolled patients diagnosed with NVAF (observation group) and non-atrial fibrillation (control group), hospitalized in Fuwai Hospital of Chinese Academy of Medical Sciences from October 2018 to June 2019, and assessed the two groups for AT-Ⅲ, protein C, protein S, and lipid levels including lipoprotein (a), three acyl glycerin (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C). Based on the CHA2DS2-VASc score, patients with NVAF and a score of less than 2 were assigned to the low-and middle-risk groups; the high-risk group consisted of patients with a score of 2 or more. The diagnostic performance of AT-Ⅲ was evaluated using receiver operating characteristic (ROC) curve analysis, and the risk factors for high CHA2DS2-VASc scores were analyzed using logistic regression.Results:Overall, 206 cases were enrolled in the observation group, including 54 women (26%; aged 59.85±11.06 years). The control group consisted of 76 cases, with 19 women (25%; aged 59.34±9.84 years). The two groups were gender ( χ2=0.043, P=0.836) and age ( t=0.352, P=0.725) matched. In the observation group, AT-Ⅲ activity (98.68%±11.37%) was significantly lower than that in the control group (110.87%±13.91%), demonstrating a statistically significant difference ( t=-6.841, P<0.001). In total, 102 cases (49.5%) were assigned to the high-risk group, with 104 cases (50.5%) in the low-and medium-risk groups. In the high-risk group, the AT-Ⅲ activity (93.67%±9.92%) was significantly lower than that in the low-and middle-risk groups (103.60%±10.56%), with a statistically significant difference observed ( t=6.953, P<0.001). In the high-risk group, protein C ［(94.34±26.61)% vs. (102.63±22.74)%］, TC ［(4.09±1.02) mmol/L vs. (4.69±0.97) mmol/L］, and LDL-C ［(2.18±0.83) mmol/L vs. (2.74±0.88) mmol/L］ levels were lower than those observed in the low-risk group (P<0.05). For NVAF screening, the AT-Ⅲ early warning threshold was 96.5%, and the area under the ROC curve was 0.746 (95% CI: 0.681-0.812, P<0.001). Based on logistic regression analysis, low AT-Ⅲ activity levels were an independent risk factor for high CHA2DS2-VASc scores in NVAF ( OR=7.282，95% CI: 3.098-17.117， P<0.001). Additionally, logistic regression analysis demonstrated that with increasing age ( OR=44.339, 95% CI: 15.207-129.276), lower levels of AT-Ⅲ ( OR=7.282, 95% CI: 3.098-17.117) and TC ( OR=4.349, 95% CI: 1.739-10.875), and higher CHA2DS2-VASc scores were observed for non-valvular AF ( P<0.05). Conclusion:A positive correlation exists between the CHA2DS2-VASc score and old age, low AT-Ⅲ activity, and low TC levels, indicating a high reference value for evaluating thrombosis in NVAF.