Neutrophil-to-lymphocyte ratio as a harbinger of peritonitis in peritoneal dialysis: a case–control study

Background: The neutrophil-to-lymphocyte ratio (NLR) is a biomarker of systemic inflammation and has been associated with adverse outcomes in dialysis patients. Its role in predicting the future risk of peritoneal dialysis-associated peritonitis (PDAP) before clinical onset remains unclear. Objective: To evaluate the association between pre-peritonitis NLR levels and the risk of developing PDAP. Methods: We conducted a retrospective, matched (1:1) case-control study involving patients on peritoneal dialysis at a single center between January 2010 and October 2024. Cases were patients who developed a first episode of PDAP (diagnosed per ISPD guidelines). Controls were matched to cases on sex and age (±3 years). The exposure was NLR measured from routine blood tests during a 3-month period preceding the peritonitis event for cases, or a corresponding pre-index period for controls. Logistic regression analysis was used to assess the association. Results: < 0.001; P for trend < 0.001). Restricted cubic spline analysis revealed a significant linear dose-response relationship (P for non-linearity = 0.511). An elevated NLR (≥ median) also showed moderate discriminative ability for predicting PDAP, with an area under the curve (AUC) of 0.78 (95% CI: 0.71-0.85). Conclusion: A higher NLR measured during a clinically stable period prior to infection is associated with an increased risk of subsequent PDAP. If validated in prospective studies, NLR may serve as a simple and readily available biomarker for risk stratification in this population.