A drop of blood, a hint of risk: neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) as early predictors and risk stratifiers in pyogenic spondylodiscitis

Introduction: Pyogenic spondylodiscitis (PSD) is a severe spinal infection with potential for significant morbidity. Early identification of patients at risk for poor outcomes is crucial. This study investigated the prognostic value of neutrophil-to-lymphocyte ratio (NLR) and platelet- to-lymphocyte ratio (PLR) at Emergency Department (ED) admission. Materials and methods: This retrospective, single-center cohort study included 187 patients diagnosed with PSD or vertebral osteomyelitis (VO) between January 2017 and December 2023. NLR and PLR were calculated from routine blood tests at admission. Outcomes included prolonged hospitalization (> 15 days), 90-day readmission, and one-year mortality. ROC analysis determined optimal cut-offs for NLR (7.78) and PLR (174.2). Multivariate logistic regression assessed the association of elevated ratios with outcomes. Results: Elevated NLR and PLR at admission were significantly associated with adverse outcomes. Patients with NLR > 7.78 had a 2.1-fold increased risk of prolonged hospitalization (95% CI 1.08–4.07), a 1.7-fold higher risk of 90-day readmission (95% CI 1.01–2.94), and a 2.4-fold increased risk of one-year mortality (95% CI 1.18–5.07). Similarly, PLR > 174.2 was associated with a 1.8-fold increased risk of prolonged hospitalization (95% CI 1.01–3.28) and a 1.8-fold increased risk of one-year mortality (95% CI 1.02–3.42). Patients with both elevated NLR and PLR had a 3.4-fold increased risk of prolonged hospitalization, a 2.4-fold increased risk of 90-day readmission, and a 3.3-fold increased risk of one-year mortality. Conclusions: Elevated NLR and PLR at ED admission are independent predictors of adverse outcomes in patients with PSD/VO. These simple hematological markers may serve as valuable tools for early risk stratification and warrant further investigation for integration into clinical management pathways.