Neutrophil-lymphocyte ratio (NLR)

The neutrophil-lymphocyte ratio (NLR) is derived from a standard complete blood count as the absolute neutrophil count divided by the absolute lymphocyte count, with a typical reference range of approximately 1–3 in healthy adults. It reflects the balance between the innate (neutrophil-driven) and adaptive (lymphocyte-driven) arms of the immune system: higher NLR indicates relative dominance of innate proinflammatory activity and/or suppression of adaptive immunity. Elevated NLR is associated with worse prognosis in a broad range of cancers, higher incidence of cardiovascular events, chronic kidney disease, and metabolic syndrome, and independently predicts all-cause mortality in large population cohorts. Physiologically, NLR rises sharply during acute stress, infection, or corticosteroid use, but persistently elevated values at rest are a marker of chronic inflammaging and immune senescence, making it a useful, cost-free index derived from routine laboratory data.