Pneumonia Risk in Severe COPD Linked to Elevated Eosinophil Count

Eosinophilic chronic obstructive pulmonary disease (COPD) with severely impaired lung function was associated with a high risk for pneumonia hospitalizations, according to the results of a study published in the European Respiratory Journal.

Signe Vedel-Krogh, PhD, from the Department of Clinical Biochemistry, Herlev and Gentofte Hospital, Copenhagen University Hospital, Denmark, and colleagues investigated whether or not high blood eosinophil counts are associated with a high risk for pneumonia in individuals with severe COPD. They analyzed data from 7180 individuals with COPD, including 643 with forced expiratory volume in 1 second (FEV₁) <50% of the predicted value from the Copenhagen General Population Study from 2003 to 2011. All primary discharge diagnoses of pneumonia during follow-up were recorded.

The multivariable adjusted incidence rate ratio was 2.17 (95% CI, 1.31-3.58) for pneumonia in individuals with COPD and an FEV₁ <50% of the predicted value compared with individuals with blood eosinophil counts at ≥0.34×10⁹/L vs <0.34×10⁹/L. A higher proportion of patients with COPD and a blood eosinophil count of ≥0.34×10⁹/L had elevated markers of low-grade systemic inflammation regardless of FEV₁. In patients with clinical COPD, defined by ≥1 recent exacerbation, ≥10 pack-years, and FEV₁ <70% of the predicted value, the incidence rate ratio was 4.52 (95% CI, 2.11-9.72). However, the risk for pneumonia did not differ by blood eosinophil count in those with COPD and an FEV₁ ≥50% of the predicted value.

The authors noted that few studies have examined the relationship between blood eosinophil count and the risk for pneumonia in patients with COPD. In addition, they argued that this relationship is important because patients with COPD who have high blood eosinophil counts are candidates for inhaled corticosteroid therapy, which is known to increase the risk for pneumonia in COPD.

The authors acknowledged that they could only account for pneumonia treated in a hospital setting, and so may have missed less severe cases. As a result, they were not able to analyze the relationship between less severe pneumonia and blood eosinophil count. Furthermore, they could exclude the possibility that some severe exacerbations of COPD may have been misdiagnosed as pneumonia, which could have biased their results.

The authors concluded that patients with COPD with a blood eosinophil count of ≥0.34×10⁹/L and an FEV₁ <50% are at higher risk for future hospitalization with pneumonia compared with those who have the same degree of airflow limitation but a lower eosinophil count. However, they also noted that in patients with a high blood eosinophil count and an FEV₁ <50%, the use of inhaled corticosteroid therapy did not further elevate the risk for pneumonia.

Reference

Vedel-Krogh S, Nordestgaard BG, Lange P, Vestbo J, Nielsen SF. Blood eosinphil count and risk of pneumonia hospitalizations in individuals with COPD [published online April 12, 2018]. Eur Resp J. doi:10.1183/13993003.00120-2018