Absolute Eosinophil Count as a Corroborative Marker for Sepsis at ICU Admission: An Observational Study

Background Among critically ill patients, sepsis continues to be a major cause of morbidity and mortality. Timely action requires an early diagnosis, but current screening methods have limitations. One commonly available hematological metric that has gained attention as a possible indicator of systemic illness is the absolute eosinophil count (AEC). The usefulness of AEC as a corroborative marker for sepsis diagnosis at intensive care unit (ICU) admission was studied in this study, along with its correlation with scores on the Sequential Organ Failure Assessment (SOFA) and quick Sequential Organ Failure Assessment (qSOFA). Methods This observational study included 76 adult patients admitted to the ICU with suspected infection between February 7, 2025, and March 31, 2026. Sepsis was classified according to the Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3) criteria. SOFA and qSOFA scores were calculated, and AEC was assessed at ICU admission. Receiver operating characteristic (ROC) curve analysis was used to derive an optimal AEC cutoff for identifying sepsis. Eosinopenia at the study-derived cutoff was incorporated as one additional point into qSOFA to construct an exploratory modified score, qSOFA-E. Correlations between AEC and SOFA/qSOFA scores were assessed using Spearman's rank correlation coefficient. Results Among the 76 patients, 38 (50%) fulfilled the Sepsis-3 criteria, 18 (23.7%) developed septic shock, and 7 (9.2%) died during hospitalization. The optimal AEC cutoff for identifying sepsis was ≤152.5 cells/µL, with an area under the ROC curve (AUC) of 0.904 (95% CI: 0.828-0.979; p<0.001). At this cutoff, AEC demonstrated 92.11% sensitivity, 84.21% specificity, and 88.16% diagnostic accuracy. AEC showed significant inverse correlations with day-1 SOFA (r=-0.585, p<0.001), day-3 SOFA (r=-0.443, p=0.005), day-1 qSOFA (r=-0.664, p<0.001), and day-3 qSOFA (r=-0.534, p=0.001). In this study cohort, qSOFA-E demonstrated higher sensitivity and diagnostic accuracy than qSOFA alone (92.11% vs. 65.79% sensitivity; 96.05% vs. 82.89% accuracy). Conclusions AEC was associated with the presence of sepsis and with higher SOFA and qSOFA scores in this ICU cohort. Incorporation of study-derived eosinopenia into qSOFA was associated with higher diagnostic sensitivity and accuracy within the study population. These findings support further investigation of AEC as an adjunctive marker and qSOFA-E as a proposed exploratory modification. Larger multicenter studies with independent validation are required before these findings can be generalized to broader clinical practice.