Objective To analyze the relationships of serum cystatin C (Cys-C) and T helper cell 17 (TH17) related cytokines with severity of chronic obstructive pulmonary disease (COPD).

Methods A total of 150 patients with COPD in stable phase were selected as observation group, and they were divided into mild to moderate airflow limitation group (n=97) and severe to extremely severe airflow limitation group (n=53) according to the severity of airflow limitation.Another 100 healthy people in the same period were selected as control group.The expression levels of Cys-C and Th17 related cytokinesinterleukin-17A (IL-17A), IL-21 and IL-22in serum were detected.The pulmonary function indexesforced expiratory volume in the first second to forced vital capacity (FEV₁/FVC) and the percentage of forced expiratory volume in the first second to the predicted value (FEV₁%pred)as well as the expression levels of serum Cys-C and Th17 related cytokines were compared between the control group and the observation group.The predictive efficacy of serum Cys-C combined with TH17 related cytokines for acute exacerbation of COPD was analyzed by receiver operating characteristic (ROC) curve.

Results Compared with the control group, the predicted percentage of FEV₁/FVC and FEV₁%pred in the observation group were significantly lower, while the expression levels of Cys-C, IL-17A, IL-21 and IL-22 in serum were significantly higher(P < 0.05).The percentage of FEV₁/FVC and FEV₁%pred in the severe to extremely severe airflow limitation group were significantly lower than those in the mild to moderate airflow limitation group, while the expression levels of Cys-C, IL-17A, IL-21 and IL-22 in serum were significantly higher than those in the mild to moderate airflow limitation group (P < 0.05).Pearson correlation analysis showed that the percentage of FEV₁/FVC and FEV₁%pred were significantly negatively correlated with expression levels of Cys-C, IL-17A, IL-21 and IL-22 in serum in COPD patients (P < 0.05).Among the 150 COPD patients, 141 cases were followed up for 6 months, with a follow-up rate of 94.00%; among them, 113 cases had acute exacerbation, while 28 cases did not have acuteexacerbation.The expression levels of Cys-C, IL-17A, IL-21 and IL-22 in serum in the acute exacerbation group were significantly higher than those in the no acute exacerbation group (P < 0.05).ROC curve analysis showed that the optimal cutoff values of serum Cys-C, IL-17A, IL-21 and IL-22 for predicting acute exacerbation of COPD were 1.49 mg/L, 37.95 ng/L, 155.43 pg/mL and 46.81 pg/mL respectively, and the area under the curve (AUC) was 0.665(95%CI, 0.419 to 0.911), 0.580(95%CI, 0.310 to 0.850), 0.710(95%CI, 0.477 to 0.943) and 0.680(95%CI, 0.427 to 0.933) respectively; the AUC of combination of four indexes for predicting acute exacerbation of COPD was 0.910(95%CI, 0 to 1.00), with a sensitivity of 65.41% and a specificity of 89.73%.

Conclusion Serum Cys-C and Th17 related cytokines are closely related to pulmonary function in COPD patients, and the combined detection of multiple indicators has certain value in predicting acute exacerbation of COPD.