Automated immature granulocyte count as a specific rule-in marker for bacteremia in the emergency department: A retrospective cohort study of 1418 patients

Rapid identification of bacteremia in the emergency department is critical for initiating timely antimicrobial therapy. While blood culture remains the gold standard, its diagnostic delay necessitates reliable surrogate markers. Traditional biomarkers like white blood cell (WBC) count offer high sensitivity but are often nonspecific, leading to unnecessary antibiotic use. This study evaluated whether the automated Immature Granulocyte (IG) count could serve as a specific rule-in marker for bacteremia. We conducted a retrospective cohort study analyzing 1418 adult patients who underwent simultaneous blood culture and complete blood count sampling at a regional teaching hospital in Taiwan throughout 2023. Patients were categorized into bacteremia (positive culture) and non-bacteremia groups. The diagnostic performance of IG% was compared with WBC, neutrophil-lymphocyte ratio, and qSOFA scores. Of the 1418 patients, 457 (32.2%) had confirmed bacteremia. While WBC (>12,000/μL) demonstrated high sensitivity (90.4%), its specificity was poor (21.7%). In contrast, an IG cutoff of >2.0% yielded a significantly higher specificity of 72.1% (sensitivity: 35.2%). Receiver operating characteristic curve analysis indicated that while IG had a modest overall area under the curve (0.51), its distribution in bacteremic patients was notably skewed towards higher values, supporting its utility as a confirmatory marker. Automated IG% exhibits superior specificity compared to traditional screening markers. We propose a 2-step strategy utilizing WBC for broad screening and IG% for targeted confirmation. Future prospective, multicenter studies are warranted to validate these findings and further evaluate the clinical impact of incorporating IG% into sepsis diagnostic algorithms.