Abstract: Objective  To investigate the predictive value of serum Clara cell secretory protein (CC16), procalcitonin (PCT) and fractalkine (FKN) levels in frailty of patients with chronic obstructive pulmonary disease (COPD). 
Methods  A total of 142 elderly patients with COPD admitted were selected and divided into two groups according to the score of the Frail Screening Scale at admission: a frailty group (n=43, with a score of 3-5), and a non-frailty group (n=99, with a score of less than 3). Another 43 patients were randomly selected as the control group. The differences in pulmonary function, serum CC16, PCT and FKN levels between the two groups were compared. Pearson correlation was used to analyze the correlation between blood indicators and pulmonary function of patients with COPD. Logistic regression analysis was used to analyze the influencing factors of COPD patients' frailty, and the value of positive indicators in predicting the risk of frailty was analyzed by using the receiver operating characteristic (ROC) curve. 
Results  The levels of serum CC16 in frailty group were significantly lower than those in the control group, while the levels of PCT and FKN were significantly higher than those in the control group (P＜0.05). The levels of forced expiratory volume in one second (FEV1), forced vital capacity (FVC) and FEV1/FVC in patients with COPD and frailty were significantly lower than those in the control group (P＜0.05). Pearson correlation analysis showed that serum CC16 was positively correlated with pulmonary function indicators (P＜0.05), while serum PCT and FKN levels were negatively correlated with pulmonary function (P＜0.001). Logistic regression analysis showed that the serological indicators CC16, PCT, FKN were all factors affecting the frailty of COPD patients, among which CC16 was a protective factor (P＜0.05). CC16, PCT, and FKN levels were closely associated with frailty of elderly patients with COPD, which could be used as predictive indicators. ROC curve analysis showed that the area under ROC curve (AUC) of PCT was the largest, which was 0.890 (0.824-0.956), followed by FKN ［0.830 (0.742-0.914)］, and CC16 (0.771). All three indicators had the value of predicting the frailty of elderly COPD patients (P＜0.05). 
Conclusion  The levels of serum CC16, PCT and FKN are closely related to the occurrence of frailty in elderly patients with COPD, and can be used as detection indicators to predict the risk of frailty. 

Key words: pulmonary disease, chronic obstructive, procalcitonin, uteroglobin