Background: Eosinophilic chronic obstructive pulmonary disease (COPD) may represent a distinct disease phenotype. The aim of this study was to investigate the occurrence of eosinophilia in the next exacerbation of patients experiencing a severe acute exacerbation of COPD (AECOPD).

Methods: Clinical parameters were measured in AECOPD patients (n=179), first at the time of hospital admission, and again at discharge following treatment. Patients were divided into eosinophilic (n=39) and noneosinophilic (n=140) groups based on blood eosinophil count results on admission. Patients were followed for 3 years to phenotype the next relapses. Data are presented as mean with SEM or median with IQR.

Results: Eosinophilic AECOPD patients (?2% and/or ?200 cells/µL) had lower C-reactive protein levels and more pronounced improvement in FEV1 after treatment compared to noneosinophilic subjects (p<0.05 for each). The proportion of patients having no or at least one relapse during follow-up did not differ between eosinophilic (46.2 vs. 53.8%) and noneosinophilic (39.3 vs. 60.7%) groups (p=NS). However, while only 47.6% of patients with eosinophilic exacerbation had an eosinophilic relapse, the majority of noneosinophilic patients (81.2%) suffered from a similar type of exacerbation as the next episode (p<0.05). Rate of exacerbations was comparable in the eosinophilic and noneosinophilic groups (0.762±0.108 vs. 0.898±0.076, p>0.05). The median time to first eosinophilic and noneosinophilic relapses was also similar (174 [52-277] vs. 186 [70-436] days, p>0.05).

Conclusions: The noneosinophilic phenotype may be more stable than the eosinophilic ones in patients experiencing severe relapses of AECOPD.