Diagnostic Utility of Neutrophil-to-Lymphocyte Ratio and Platelet-to-Lymphocyte Ratio in Acute Inflammatory and Infectious Disorders

Abstract

Background: Rapid identification of infection and assessment of inflammatory severity are important for early clinical decision-making. Neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) are inexpensive inflammatory indices derived from routine complete blood counts. This study evaluated their diagnostic utility in acute inflammatory and infectious disorders.

Methods: This prospective observational diagnostic study included 150 adults with acute infectious or noninfectious inflammatory disorders. NLR and PLR were calculated from initial complete blood counts and compared with clinical diagnosis, C-reactive protein (CRP), and disease severity. Receiver operating characteristic (ROC) analysis was used to determine diagnostic performance, and multivariate logistic regression identified predictors of severe disease.

Results: Infectious disorders were diagnosed in 96 (64.0%) patients, while 54 (36.0%) had noninfectious inflammatory disorders. Median NLR was significantly higher in infectious than noninfectious conditions [6.72 vs 3.61; p<0.001], as was PLR [189.6 vs 139.2; p<0.001]. Patients with severe disease had significantly higher NLR (9.18 vs 4.31) and PLR (229.4 vs 149.8; both p<0.001). NLR correlated positively with CRP (r=0.56; p<0.001). For identifying infectious disorders, NLR >4.8 demonstrated an AUC of 0.82, sensitivity of 79.2%, specificity of 72.2%, and accuracy of 76.7%, whereas PLR had an AUC of 0.73. On multivariate analysis, NLR >7 independently predicted severe disease (AOR 3.26; 95% CI: 1.54–6.90; p=0.002).

Conclusion: NLR demonstrated good diagnostic utility for identifying infectious disorders and was independently associated with disease severity. NLR may provide a rapid, inexpensive, and readily available adjunct to conventional inflammatory biomarkers.