Neutrophil–lymphocyte ratio as a predictor of adverse outcome in patients with community‐acquired pneumonia: A systematic review

BACKGROUND: Community‐acquired pneumonia (CAP) is the acute infection of lung tissue in an immunocompetent who acquired it from the community. Its incidence and mortality are significant and require a marker to predict the severity and mortality in these patients. Neutrophil–lymphocyte ratio (NLR) is a simple, cheap, and easy‐to‐use marker and this study describes its role in predicting the adverse outcome in patients with CAP. METHODS: PubMed, EMBASE, and Google Scholar were used to search for related studies on February 8, 2021. A total of 186 articles were retrieved upon detailed searching in the databases and search engines. After a series of removing duplicate articles, title and abstract screening, and full‐text review; nine articles were found eligible and included in the study. The data from each article were collected in MS Excel and the findings were summarized in this manuscript. RESULTS: The total number of patients analyzed in this systematic review is 3340. The mean age of the patient in the included studies ranged from 61 to 90.4 years. All studies had adverse outcomes as the endpoint of the study, which included in‐hospital mortality or intensive care unit (ICU) admission or deterioration from medium and low risk to high risk or 30 days' mortality. The prevalence of endpoint ranged from 5.8% to 44.8%. NLR with a cutoff value of more than 10 was shown to predict mortality compared to C‐reactive protein levels, white blood cell count, neutrophil count, lymphocyte level, Pneumonia Severity Index (PSI) level, PSI class, procalcitonin, and CURB‐65 (Confusion, Respiratory rate, Blood pressure, 65 years of age and older) in most of the studies. CONCLUSION: NLR is a simple, easily measured yet promising marker for predicting outcomes in patients with CAP.