Monocyte Distribution Width as a Biomarker for Predicting Bacteremia: A Retrospective Study in the Emergency Department

Blood culture is the diagnostic gold standard for bacteremia in the emergency department (ED), but its turnaround time can delay appropriate antimicrobial therapy, highlighting the need for rapid, accessible biomarkers. We retrospectively analyzed adult ED patients from July 2023 to June 2024 who underwent blood culture testing and had complete data for monocyte distribution width (MDW), white blood cell count (WBC), C-reactive protein (CRP), and neutrophil-to-lymphocyte ratio (NLR). Discrimination was assessed using area under the receiver operating characteristic curve (AUROC) and diagnostic accuracy using sensitivity, specificity, and diagnostic odds ratio (DOR); combined models were compared with net reclassification improvement (NRI) and integrated discrimination improvement (IDI). Among 19,325 patients, 2011 (10.4%) had positive blood cultures. MDW had the highest AUROC (0.760) versus CRP (0.730), NLR (0.695), and WBC (0.642); at a cut-off of 22, MDW showed 0.72 sensitivity, 0.68 specificity, and DOR 5.46. The best combined model was MDW+NLR (AUROC 0.785; DOR 6.39; NRI 0.428; IDI 0.770). MDW is a rapid and effective marker for identifying bacteremia in the ED, and performance improves when combined with NLR.