Usefulness of the Neutrophil-Lymphocyte Ratio as a Prognostic Marker in Systemic Infections

The neutrophil-to-lymphocyte ratio (NLR) is an inflammatory biomarker derived from the complete blood count that reflects the dynamic balance between innate and adaptive immunity. In recent years, multiple studies have demonstrated its prognostic utility in systemic infections, particularly in sepsis, community-acquired pneumonia, and COVID-19. Its low cost, wide availability, and rapid assessment make it an attractive tool in both high- and low-resource settings. This review analyzes the pathophysiological basis of NLR, available clinical evidence, reported cutoff values, comparison with other biomarkers, and its main limitations. NLR represents a complementary prognostic marker with independent value in predicting severity and mortality in systemic infections.