Neutrophil to lymphocyte ratio is a better indicator of COPD exacerbation severity in neutrophilic endotypes than eosinophilic endotypes

BACKGROUND: Complete blood count parameters provide novel inflammatory markers, namely neutrophil to lymphocyte ratio (NLR) and platelet to lymphocyte ratio (PLR). We aimed to assess any differences in these novel inflammatory markers according to exacerbation severity in patients with COPD in both eosinophilic and neutrophilic endotypes. METHOD: This retrospective cross-sectional study was conducted at a tertiary education hospital. Previously diagnosed COPD patients admitted to the hospital with acute COPD exacerbation (AECOPD) were enrolled into the study. Patients were grouped according to COPD endotype, eosinophilic (peripheral blood eosinophil rate ≥2%) and neutrophilic (peripheral blood eosinophil rate <2%), and further subdivided according to place of admission (outpatient clinic, ward, or intensive care unit [ICU]) as an indicator of disease severity. Complete blood count, biochemistry, C-reactive protein (CRP), NLR, PLR, and platelet to mean platelet volume values were recorded from an electronic hospital database system and compared among all groups. RESULTS: Of the 10,592 patients included in the study, 7,864 were admitted as outpatients, 2,233 to the wards, and 495 to ICU. Neutrophilic COPD patients (n=6,536, 62%) had increased inflammatory markers compared with eosinophilic COPD patients (n=4,056, 38%); median NLR was 5.11 vs 2.62 (P<0.001), PLR was 175.66 vs 130.00 (P<0.001), and CRP was 11.6 vs 7.7 (P<0.001). All values increased relative to admission to the outpatient clinic, ward, or ICU: median NLR was 3.20, 6.33, and 5.94, respectively, median PLR was 140.43, 208.46, and 207.39, respectively, and median CRP was 6.4, 15.0, and 22.8, respectively. The median NLR values of patients in outpatients/ward/ICU increased in neutrophilic and eosinophilic endotypes: 4.21/7.57/8.60 (P<0.001) and 2.50/3.43/3.42 (P=0.81), respectively. CRP showed a similar increased pattern according to severity of AECOPD endotypes. CONCLUSION: In COPD exacerbation, the inflammatory markers show different increases in each COPD endotypes. These findings may be crucial for defining exacerbation endotypes, the severity of exacerbation, and treatment response during follow-up in COPD patients.