Associations of Serum Urea With Neutrophil-to-Lymphocyte Ratio in Lung Cancer Patients

Systemic inflammation and metabolic alterations frequently coexist in lung cancer, yet their interrelationship remains incompletely understood. Serum urea is routinely measured in clinical practice but is rarely examined in relation to immune-inflammatory indices. We conducted a retrospective cross-sectional analysis of lung cancer patients with available serum urea and complete blood count data. Associations between serum urea and inflammatory immune indices, including the neutrophil-to-lymphocyte ratio (NLR), were evaluated using non-parametric correlation analyses. Multivariable regression and exploratory mediation analyses were performed to assess the contribution of lymphocyte count to observed associations. Eighty-three patients were included in the final analysis. Serum urea was positively associated with NLR and inversely associated with absolute lymphocyte count. Serum creatinine did not demonstrate a comparable association with NLR. Exploratory mediation analysis suggested that lymphocyte count partially mediated the association between serum urea and NLR. Sensitivity analyses excluding explicitly treated patients and additional adjustment for hepatic biochemical markers did not materially alter the findings. In patients with lung cancer, higher serum urea levels are associated with systemic immune dysregulation, reflected by elevated NLR and lower lymphocyte counts. These findings suggest that serum urea may serve as an integrative marker of metabolic-immune coupling beyond its conventional interpretation as a marker of renal function. Further longitudinal studies are warranted to clarify the clinical implications of this association.