ObjectiveTo analyze the correlation between the sarcopenia index (the ratio of creatinine to cystatin C, CCR) and the severity of chronic obstructive pulmonary disease (COPD), and evaluate its potential value as an indicator for auxiliary diagnosis of COPD and assessment of disease severity. Methods A total of 315 patients who underwent pulmonary function tests at Tongren People's Hospital from January 2022 to December 2022 were selected. Among them, 180 patients were diagnosed with COPD, and 135 patients were non-COPD. The COPD group was further divided into GOLD1 group (mild, n=36), GOLD2 group (moderate, n=70), and GOLD3 group (severe, n=74) according to Chronic Obstructive Lung Disease (GOLD) classification. The clinical data, laboratory indicators, and pulmonary function test results of the patients were collected. Correlation analysis was used to explore the correlation between CCR and clinical data. Binary logistic regression analysis was used to explore the influencing factors of COPD. A receiver operating characteristic curve was drawn, and the area under the curve (AUC) was calculated to evaluate the predictive value of CCR for COPD. ResultsAmong the 315 enrolled patients, the prevalence of COPD was 57.14% (180/315). The CCR level of the COPD patients was significantly lower than that of the non-COPD patients. The more severe the condition of COPD patients, the lower the CCR value. The results of Spearman correlation analysis showed that CCR was significantly positively correlated with diffusion capacity of the lung for carbon monoxide, forced expiratory volume in the first second (FEV1) as a percentage of predicted value, FEV1/forced vital capacity, albumin, eosinophils, endogenous creatinine clearance rate, low-density lipoprotein cholesterol, and haemoglobin, and significantly negatively correlated with C-reactive protein, D-dimer, age, and neutrophil to lymphocyte ratio (all P<0.05). Binary logistic regression showed that after adjusting for other relevant factors, CCR was found to be an independent risk factor for the occurrence of COPD (OR=0.902, 95%CI 0.879 - 0.925, P<0.05). When the CCR value was 77.450, the AUC was 0.841 (95%CI 0.798 - 0.885), with a sensitivity of 60.7% and a specificity of 96.1%.ConclusionCCR is closely related to the disease condition and its severity in patients with stable-phase COPD, and it is an independent influencing factor for the occurrence of COPD.