NEUTROPHIL-TO-LYMPHOCYTE RATIO (NLR) AS A DIFFERENTIAL MARKER BETWEEN COVID-19 AND INFLUENZA: A RETROSPECTIVE DOCUMENTARY STUDY

Abstract

Introduction: Respiratory syndromes caused by SARS-CoV-2 and influenza virus present similar clinical manifestations, making early differential diagnosis challenging. In Brazil, covid-19 circulates with significant regional variation, whereas influenza has a worldwide distribution and distinct seasonality across regions of the globe. The neutrophil-to-lymphocyte ratio (NLR) has been described as a simple, low-cost marker already available in the complete blood count, with potential clinical utility. Objective: To evaluate the NLR as a differential marker between covid-19 and influenza, comparing covid-19 data from the regions of Brazil with influenza data from around the world. Methodology: This was a documentary, retrospective, quantitative study based on secondary data extracted from published scientific articles. Brazilian articles on covid-19 with data from different regions of the country and articles on influenza from various parts of the world were selected. Results: No statistically significant difference was observed between NLR values in the covid-19 and influenza groups in the comparisons performed (p > 0.05). In addition, the direction of the difference varied according to whether the NLR reported by the studies or the NLR recalculated from neutrophil and lymphocyte counts was used. Conclusion: The results do not support the use of NLR alone as a differential marker between covid-19 and influenza. NLR remains relevant as an auxiliary marker of severity and prognosis within each disease and should be interpreted together with clinical data and specific laboratory tests.