Neutrophil-to-lymphocyte Ratio in Acute Exacerbation of Chronic Obstructive Pulmonary Disease - Need for Population Based Cutoff Values

Sir, In July–September 2024 issue of the journal, Jain et al.[1] compared the neutrophil-to-lymphocyte ratio (NLR) between stable chronic obstructive pulmonary disease (COPD) patients and acute exacerbation COPD (AECOPD) patients and defined the correlation of NLR with the AECOPD severity. Jain et al.[1] pointed out that NLR could be utilized as a marker of AECOPD among Indian patients since it was significantly increased in AECOPD patients and within normal ranges in stable COPD patients. We have two comments on that study. Jain et al.[1] mentioned two study limitations that might question the study results, namely the small sample size and lack of serial NLR measurements to assess the prognosis and predictive outcomes. We address another important limitation. In clinical studies, the cutoff value (COV) is often employed to denote a value representing the lowest point at which a certain health threat is attained. To use the novel marker of NLR in enhancing the risk stratification on hospital admission for COPD patients and targeting the institution of aggressive versus supportive treatments, there is a need to refer to the NLR COV. A systematic review and meta-analysis revealed that NLR elevation was correlated with AECOPD diagnosis. Although the pooled NLR specificity, sensitivity, and area under the curve were 0.73 (95% confidence interval [CI]: 0.65–0.80), 0.71 (95% CI: 0.64–0.77), and 0.78 (95% CI: 0.74–0.81), respectively,[2] certain populations have interestingly developed their NLR COV for increased propensity to AECOPD to be referred to in clinical setups and research.[3,4] Regrettably, Jain et al.[1] did not estimate NLR COV for the studied COPD Indian population. Consequently, the clinical applicability of study findings within the Indian context might be further hindered by this limitation. Second, apart from NLR, platelet-to-lymphocyte ratio, monocyte-to-lymphocyte ratio, and eosinophil-to-lymphocyte ratio were recently found to serve as useful biomarkers in AECOPD patients.[5] Conducting future comparative studies in India to define which biomarker is the best for care and follow-up of COPD patients is solicited. Author contribution statement MDA-M: Design, concept, literature review, preparation and editing of the manuscript, and final approval. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.