Age and Sex Influence the Neutrophil-to-Lymphocyte Ratio (NLR), a Systemic Inflammation Marker

Background/Objectives: The neutrophil-to-lymphocyte ratio (NLR), as a marker of systemic inflammation, has been studied in a wide variety of diseases. Unfortunately, there are very limited data describing the NLR distribution and reference intervals for a normal population in specific geographical areas. The aim of this study was to analyze, for the first time, different patterns in NLR distribution, stratified by age and sex, in a large group of controls from a European country. Methods: Patients referred for a health examination to the Laboratory Department of Dr Negrín University Hospital from 1 January 2021 to 31 December 2025 were included in this study. The participants had normal hematological values, lipid metabolism markers and hepatic enzymes, erythrocyte sedimentation rates (ESRs), and C-reactive protein (CRP) levels. Samples were treated anonymously, including only sex and date of birth. The neutrophil-to-lymphocyte ratio (NLR) was determined by dividing the absolute neutrophil count by the absolute lymphocyte count. Results: A total of 30,676 controls were included in the study. NLR increased with age (p < 0.0001). Women showed lower NLR values than men (p < 0.0001), revealing an age-related pattern, with values increasing until age 45, dropping from 46 to 65, and slightly increasing in advanced age (>65 years). Conclusions: To our knowledge, this is the largest study from a European country analyzing the impact of sex and age on NLR values in controls. An interesting differential pattern of NLR modifications according to age group was observed in women. Therefore, NLR values must always be interpreted according to sex and age groups.