Low, high eosinophil counts linked to greater bronchiectasis, exacerbation severity

Key takeaways:

• The relationship between blood eosinophil count and bronchiectasis severity was U-shaped, meaning greater severity with low and high counts.
• This shape also appeared between eosinophil count and exacerbations.

Among patients with bronchiectasis, disease severity was higher with a blood eosinophil count less than 50 cells/μL or higher than 300 cells/μL, according to results published in CHEST.

Further, between the two groups, the group with the lower count had greater disease and exacerbation severity, according to researchers.

“According to our results, both the group with bronchiectasis and eosinopenia (defined as < 50 cells/μL) and the one with eosinophilia (defined as > 300 cells/μL) showed greater disease severity and a greater number and severity of exacerbations than the group with eosinophil counts between these two figures,” Miguel Ángel Martínez-García, MD, of the department of respiratory medicine at La Fe University and Polytechnic Hospital and the Biomedical Network Research Center at the Carlos III Health Institute in Spain, and colleagues wrote.

In a multicenter, prospective observational study using the Spanish Bronchiectasis Registry, Martínez-García and colleagues assessed 928 adults (mean age, 67.5 years; 64.7% women) with bronchiectasis and a blood eosinophil count (BEC) to determine how BEC is linked to disease severity, exacerbations and inhaled corticosteroid treatment.

Researchers grouped patients based on their number of eosinophils. Of the total cohort, 123 patients (13.3%) had eosinopenic bronchiectasis (< 50 cells/μL), 164 patients (17.7%) had a low number of eosinophils (51-100 cells/μL), 488 patients (52.6%) had a normal number of eosinophils (101-300 cells/μL) and 153 patients (16.5%) had eosinophilic bronchiectasis (> 300 cells/μL).

At baseline, several characteristics were higher in the eosinopenia and eosinophilia groups vs. the low and normal eosinophil number groups: overall bronchiectasis severity, prevalence of chronic bronchial infection by Pseudomonas aeruginosa, inhaled antibiotic and macrolide use, number and severity of exacerbations, and inhaled corticosteroid treatment use.

In contrast, FEV1 was higher in the low and normal eosinophil number groups, according to researchers.

Researchers used three scores to assess disease severity, including FACED (FEV₁, Age, Chronic infection by P. aeruginosa, Extension [radiological lobes affected] and Dyspnea), Exacerbations-FACED and the Bronchiectasis Severity Index (BSI). In each of these scores, significantly greater severity was found among patients with eosinopenia vs. patients with eosinophilia.

Notably, the relationship between BEC and bronchiectasis severity was U-shaped.

Similar to the above results, researchers observed a U-shaped relationship between BEC and exacerbations, with a significant increase in hospitalizations (P = .032) and the number of exacerbations (P = .012) among patients with eosinopenia vs. eosinophilia.

Between the low and normal number of eosinophils groups, disease severity did not significantly differ, but researchers found significantly more hospitalizations and exacerbations in the low number group (exacerbation severity, P = .022; exacerbation number, P = .044).

Among those who received inhaled corticosteroid treatment, patients with the highest eosinophil counts had significant reductions in the number of hospitalizations (1.2 vs. 0.7; P = .011). as well as the number of exacerbations (2.2 vs. 1.5; P = .017). Researchers noted that this outcome was only observed in this group.

Of the four groups, the eosinophilic bronchiectasis group had the most patients with exacerbations (54.6%), and researchers found a heightened risk for frequent exacerbations (minimum of three exacerbations per year) in this group (HR = 1.28; 95% CI, 1.1-2.1) vs. the group with a normal number of eosinophils.

Notably, the risk for frequent exacerbations was even higher in the eosinopenia group vs. the group with a normal number of eosinophils (HR = 2.4; 95% CI, 1.6-3.7).

“The relationship between the BEC and the severity of bronchiectasis presents (from the functional, microbiological and exacerbations viewpoints) a U-shaped relationship (an inverted U in the case of FEV₁), whereas the group with [less than] 50 eosinophils/μL showed the greatest severity,” Martínez-García and colleagues wrote.