The Value of First-Day CRP and NLR in Distinguishing Infectious from Non-Infectious Causes of Loss of Consciousness in the Emergency Department.

Background: Altered level of consciousness (ALOC) is a common presentation in the emergency department (ED) with a broad spectrum of infectious and non-infectious etiologies and is associated with substantial morbidity and mortality. Early identification of infectious causes is therefore critical for timely management. C-reactive protein (CRP) and the neutrophil-to-lymphocyte ratio (NLR) are readily available inflammatory markers that may assist in this differentiation. Methods: In this cross-sectional study, 322 patients presenting with ALOC and admitted to the ED of Baharloo Hospital were evaluated. Baseline demographic, clinical, and laboratory data were collected, and patients were classified as having infectious or non-infectious etiologies. First-day CRP and NLR values were compared between groups. Receiver operating characteristic (ROC) curve analysis assessed the diagnostic performance of CRP, NLR, and their combination in distinguishing infectious from non-infectious causes. Logistic regression analysis identified predictors of in-hospital mortality. Results: The mean age was 62 years, and 36.6% of patients had an infectious etiology. Mortality was significantly higher in the infectious group than in the non-infectious group (60.2% vs. 22.1%, p<0.001). Median CRP and NLR values were significantly higher in infectious cases (both p<0.05). CRP at a cut-off of 32.0 mg/L yielded an area under the curve (AUC) of 0.76, with 71% sensitivity and 83% specificity, outperforming NLR (cut-off 5.53; AUC 0.68, sensitivity 71%, specificity 60%). The combined model achieved an AUC of 0.79 with 76.3% sensitivity and 76.5% specificity. Multivariable logistic regression identified older age (odds ratio [OR] 1.07, 95% confidence interval [CI]: 1.04-1.09), longer hospital stay (OR 1.09, 95% CI: 1.05-1.13), lower Glasgow Coma Scale score (OR 0.67, 95% CI: 0.59-0.75), and higher NLR (OR 1.14, 95% CI: 1.02-1.27) as independent predictors of mortality. Conclusion: First-day CRP and NLR, particularly CRP, show acceptable diagnostic performance for distinguishing infectious from non-infectious causes of ALOC in the ED. Combined use of these markers improves diagnostic accuracy, and elevated NLR is independently associated with in-hospital mortality, supporting its role alongside clinical assessment for early risk stratification.