To characterize the phenotype of frequent acute exacerbations of chronic obstructive pulmonary disease (COPD), and to find biomarkers that can effectively identify this phenotype and predict the risk of acute exacerbations.

This was a prospective study that included 190 COPD patients admitted to the Department of Respiratory and Critical Care Medicine of Peking University Shougang Hospital. The patients were divided into a frequent exacerbation group (98 cases) and an infrequent exacerbation group (92 cases) according to the frequency of acute exacerbations in the year before enrollment. Then, the patients in the acute exacerbation period and stable period were monitored in each group. The levels of interleukin-8 (IL-8), leukotriene B4 (LTB4), 8-isoprostane (8-iso-PG), and eosinophils (EOS) in blood and exhaled breath condensate (EBC) were measured, and the data in different periods were analyzed between the two groups. Blood EOS were analyzed according to different counting methods (absolute value and proportion). Statistically significant indicators were identified. The frequency of acute exacerbations was recorded in a follow-up period of two years.

The median values of IL-8, LTB4, 8-iso-PG, and EOS in blood and EBC in patients who were in the acute exacerbation period were significantly higher than those in the stable stage (P<0.05). There were significant differences in the distribution of IL-8 in EBC during acute exacerbation, 8-iso-PG in blood during the stable period, and the frequency of acute exacerbations during the two-year follow-up period between the two groups. IL-8 in EBC during acute exacerbation and the annual frequency of acute exacerbations in the two years of follow-up were positively correlated with different groups (P<0.05). After grouping patients according to the absolute value of blood EOS of 100 cells/µL (0.1) and 300 cells/µL (0.3), the 8-iso-PG in EBC and LTB4 in blood during the stable stage were significant positively correlated with the different groups. After grouping blood EOS by a percentage of 2%, LTB4 in blood during the stable stage still increased significantly with the increase of blood EOS (P<0.05); however, no positive correlation was found between them. There was no correlation between EOS and the annual frequency of acute exacerbations within the three years, no matter grouped by count or percentage.

In patients with COPD, multiple inflammatory indicators are higher in the acute exacerbation phase than in the stable phase. Among them, IL-8 in EBC during the acute exacerbation period may become a biomarker that predicts the frequent acute exacerbation phenotype. The significance of blood EOS is different according to grouping methods. The 8-iso-PG in EBC and LTB4 in blood during the stable phase may be associated with eosinophilia phenotype. Blood eosinophils are not a good predictor of the risk of an acute exacerbation.