Eosinophilic and non-eosinophilic COPD patients with chronic respiratory failure: neutrophil-to-lymphocyte ratio as an exacerbation marker

Abstract

Aim: Increased dyspnea, sputum volume, and purulence are subjective symptoms in COPD patients. To diagnose COPD exacerbations with chronic respiratory failure (CRF) and to assess the requirement for antibiotic treatment, physicians require more objective criteria. We aimed to investigate whether neutrophil-to-lymphocyte ratio (NLR) can be used as an infectious exacerbation marker in COPD patients with CRF.

Patients and methods: This retrospective cross-sectional study was performed in the intensive care outpatient clinic of a tertiary training hospital between 2014 and 2015. Patients admitted with CRF due to COPD and who had complete blood count (CBC) results were enrolled. CBC results and C-reactive protein (CRP) levels were obtained from the hospital online database. The "modified exacerbation model (MEM)" was defined as follows: exacerbation A, leukocytes ≥12,000/mm³, CRP >10 mg/dL; exacerbation B, leukocytes ≥10,000/mm³, CRP >10 mg/dL; exacerbation C, leukocytes ≥10,000/mm³, CRP >8 mg/dL; exacerbation D, leukocytes ≥10,000/mm³, CRP >5 mg/dL. The cutoff value of NLR was defined for each model. Patients were split into two groups based on the NLR cutoff value according to the "NLR exacerbation model" and further subgrouped according to peripheral eosinophil percentage (eosinophils ≥2% and <2%) and compared with the MEM.

Results: A total of 1,066 COPD patients (430 females, 40.3%), with a mean age of 66±13 years, were included. A NLR cutoff value of 3.54 (NLR ≥3.54, n=366, 34%) showed the highest sensitivity and specificity for model A (78%, 69%), model B (63%, 71%), model C (61%, 72%), and model D (58%, 72%). Peripheral eosinophilia (PE ≥2%) was present in 48 patients (4.5%). The ratio of patients with PE <2% in the NLR ≥3.54 group was significantly higher in the MEM (P<0.001).

Conclusion: The NLR presents an attractive option as an exacerbation marker in COPD patients with CRF due to its simplicity and cost-effectiveness. In COPD patients with CRF, where the NLR is ≥3.54, PE levels are <2%, and subjective symptoms are present, antibiotic treatment should be considered.

Keywords: COPD; chronic respiratory failure; exacerbation; neutrophil-to-lymphocyte ratio; peripheral eosinophilia.

Figure 1

Flowchart of patient enrollment. Abbreviations: ALS, amyotrophic lateral sclerosis; CBC, complete blood count; CRF, chronic respiratory failure; CRP, C-reactive protein; ILD, interstitial lung disease; OHS, obesity hypoventilation syndrome.

Figure 2

Flowchart of MEMs in COPD patients with CRF. Notes: Exacerbation and stable groups were defined by using MEMs. Patients were grouped into two according to NLR cutoff value and evaluated for the presence of PBE. Abbreviations: CRF, chronic respiratory failure; CRP, C-reactive protein; MEM, modified exacerbation model; NLR, neutrophil-to-lymphocyte ratio; PBE, peripheral blood eosinophilia; WBC, white blood cell.

Figure 3

ROC curves, the optimal cutoff value, sensitivity, and specificity of NLR for MEMs (models A, B, C, D). Notes: ROC-AUC was used to asses “patients’ NLR value” in all four attack models. NLR cutoff value was found according to ROC curves. (A) The cutoff value, sensitivity, and specificity of NLR for exacerbation model A. (B) The cutoff value, sensitivity, and specificity of NLR for exacerbation model B. (C) The cutoff value, sensitivity, and specificity of NLR for exacerbation model C. (D) The cutoff value, sensitivity, and specificity of NLR for exacerbation model D. Diagonal segments are produced by ties. Abbreviations: AUC, area under the curve; MEM, modified exacerbation model; NLR, neutrophil-to-lymphocyte ratio; ROC, receiver operating characteristic.