COPD in never-smokers may be associated with different clinical characteristics and biomarker patterns compared with smoking-related COPD, according to a population-based study.
In the analysis, investigators included 690 participants aged 50 to 75 years from the SCAPIS study. Five groups were examined: never-smokers with COPD (n = 154), never-smokers with normal lung function (n = 281), current smokers with normal lung function (n = 97), ex-smokers with COPD (n = 103), and current smokers with COPD (n = 55). COPD was defined by postbronchodilator spirometry as a forced expiratory volume in 1 second (FEV1)/forced vital capacity ratio below the lower limit of normal.
Never-smokers with COPD had a mean age of 60 years, and 37% of them identified as female. Compared with never-smokers with normal lung function, never-smokers with COPD reported more wheeze (44% vs 18%) and productive cough (39% vs 19%). Thirty percent had a COPD Assessment Test score ≥ 10, compared with 12% among never-smokers without airflow limitation, indicating poorer health status.
Airflow limitation was generally milder in never-smokers with COPD compared with in the participants with smoking-related COPD. Mean postbronchodilator FEV1 was 87% of predicted in never-smokers with COPD, compared with 78% in ex-smokers and 79% in current smokers with COPD.
Biomarker patterns also differed between the groups. For instance, 43% of never-smokers with COPD had Immunoglobulin E (IgE) sensitization to airborne allergens. They also had higher geometric mean fractional exhaled nitric oxide (FeNO) levels (22 ppb) compared with the other groups. Peripheral blood eosinophil counts were slightly higher in the never-smokers with COPD compared with in the never-smokers with normal lung function (0.15×10⁹/L vs 0.13×10⁹/L). In contrast, the participants with a smoking history had higher leukocyte and neutrophil counts.
Self-reported asthma was more common among the never-smokers with COPD compared with among the never-smokers without COPD (40% vs 12%). When the participants with asthma were excluded, never-smokers with COPD continued to report more wheeze and cough and had higher FeNO levels, although differences in IgE sensitization and blood eosinophils were reduced.
The participants were classified based on spirometry and smoking history, regardless of symptoms. Respiratory symptoms were reported across all of the groups. Notably, 20% of never-smokers with normal lung function reported symptoms, while 20%– to 39% of the participants with smoking-related COPD reported no respiratory symptoms.
The investigators noted that the strict spirometric criteria and limited age range may have affected generalizability. Overall, the findings indicated that COPD in never-smokers differs in symptom profile, airflow limitation, and inflammatory markers from smoking-related COPD.
"Our findings suggest that never-smokers with COPD might represent a distinct clinical phenotype, which may need to be handled differently both in the diagnostic and clinical follow-up," concluded lead study author Pernilla Sönnerfors, of the Division of Immunology and Respiratory Medicine in the Department of Medicine Solna at the Karolinska Institutet in Sweden, and colleagues.
The study authors reported no competing interests.
Source: BMJ Open Respiratory Research