Predicting COPD Exacerbations Using Sputum vs Blood Eosinophils

High concentrations of sputum eosinophils may be a better biomarker than serum blood in identifying a subset of patients more susceptible to an increased severity of chronic obstructive pulmonary disease (COPD), decreased quality of life, more frequent exacerbations, and increased emphysema and air trapping, according to a study published in Lancet Respiratory Medicine.

Researchers at 6 clinical sites in the United States conducted a multicenter observational study to determine whether more frequent exacerbations and a more severe phenotype of COPD were associated with high eosinophil concentrations in either the blood or sputum of this patient population. In addition, they investigated whether sputum eosinophils could be accurately predicted by peripheral blood eosinophil counts.

Data were obtained from 2737 patients from SPIROMICS (Subpopulations and Intermediate Outcome Measures in COPD Study; ClinicalTrials.gov identifier: NCT01969344) who had COPD and were between the ages 40 and 80 years with a history of smoking at least 20 pack-years. Blood eosinophil counts from 2499 patients (1262 patients with low counts [<200 cells/μL] and 1237 with high counts [≥200 cells/μL]) who were smokers and sputum eosinophils from 827 patients (656 patients with low counts [<1.25%] and 171 patients with high counts [≥1.25%]) were available for analysis.

Study results showed a significantly lower median forced expiratory volume in 1 second percentage predicted in patients with a high sputum eosinophil count compared with patients with a low sputum eosinophil count both before and after bronchodilation (65.7% vs 75.7% [P <.0001] and 77.3% vs 82.9% [P =.001], respectively). In addition, patients in the high sputum eosinophil group experienced more exacerbations that required corticosteroid treatments compared with patients in the low sputum eosinophil group (32 [19%] of 171 vs 66 [10%] of 656; P =.002).

Patients who exhibited an increase in airway wall thickness (0.02 mm difference; P =.032) and increased wheezing (P =.018), but no increase in COPD exacerbations (P =.35), were in the high eosinophil count group. Results also demonstrated a weak but significant association between blood eosinophil counts and sputum eosinophil counts (correlation coefficient r=0.178; P <.0001), but with a high false-discovery rate of 72%.

Investigators concluded that a sputum eosinophil count is a more superior biomarker for identifying patients at a higher risk for a more severe form of COPD, more frequent exacerbations, and increased emphysema by quantitative computed tomography compared with a blood eosinophil count. A higher blood eosinophil count alone was not found to be a significant predictor of COPD exacerbations unless combined with a high sputum eosinophil count or a history of exacerbations. Therefore, clinicians should continue to use sputum eosinophil counts as a more accurate predictor of exacerbation risk in patients with COPD.

Reference

Hastie AT, Martinez FJ, Curtis JL, et al. Association of blood sputum and blood eosinophil concentrations with clinical measures of COPD severity: an analysis of the SPIROMICS cohort. Lancet Respir Med. 2017;5(12):956-967.