The role of the neutrophil-to-lymphocyte ratio in predicting outcomes among patients with community-acquired pneumonia

Objectives: The value of the neutrophil-to-lymphocyte ratio (NLR) in predicting outcomes in patients hospitalised with community-acquired pneumonia (CAP) remains debated. This study evaluated whether NLR independently predicts clinical outcomes and enhances the predictive performance of the CURB-65 score in patients with CAP. Methods: Data from CAP admissions at two Australian hospitals from 2018 to 2023 were analysed. NLR was calculated using admission neutrophil and lymphocyte counts. Patients were categorised into NLR >12 and NLR ≤12. Multilevel-multivariable regression models, adjusting for age, sex, Charlson index, CURB-65 score, Hospital Frailty Risk Score (HFRS) and C-reactive protein (CRP), assessed outcomes including length of stay (LOS), intensive care unit (ICU) admission and in-hospital mortality. Results: Over 6 years, 7,862 patients with CAP were hospitalised (mean age 75.1 years, 54.6% male). Mean NLR was 12.6, with 2,877 (36.6%) patients having an NLR >12. Those with NLR >12 were older males with higher disease severity and Charlson index (p<0.05). Adjusted analyses showed that NLR >12 was independently associated with prolonged LOS (IRR=1.11, 95% CI 1.08–1.13, p<0.001), increased risk of ICU admission (adjusted odds ratio (aOR) =1.41, 95% confidence interval (CI) 1.06–1.88, p=0.019), and higher in-hospital mortality (aOR=1.27, 95% CI 1.06–1.53, p=0.009). The predictive ability of the CURB-65 score for in-hospital mortality was good (area under the curve (AUC) 0.68, 95% CI 0.66–0.70), while it was modest for the NLR (AUC 0.58, 95% CI 0.56–0.60). Incorporation of NLR to the CURB-65 score did not enhance its predictive ability (AUC 0.69, p>0.05). Conclusions: NLR independently predicts adverse outcomes in patients hospitalised with CAP but does not improve the predictive performance of the CURB-65 score.