Diagnostic Performance of Neutrophil CD64 Combined with qSOFA Score for Early Sepsis Diagnosis in Emergency Department Patients: A Prospective Cohort Study

Background Sepsis remains a leading cause of global mortality, making early diagnosis critical for improving patient outcomes. The quick Sequential Organ Failure Assessment (qSOFA) score and neutrophil CD64 (nCD64) expression are potential diagnostic tools, yet the performance of either alone is limited. Objective This study aimed to evaluate the diagnostic accuracy of nCD64 combined with the qSOFA score in patients with suspected infection and to explore its prognostic value. Methods This prospective cohort study was registered at the Chinese Clinical Trial Registry (ChiCTR2500111783). Conducted at a Chinese hospital between 2023 and 2025, it enrolled 210 patients with suspected infection (114 with sepsis, 96 without sepsis). Baseline data were collected, including nCD64 (measured by flow cytometry), qSOFA score, and other biomarkers. A combined index was calculated using data-driven weight optimization (nCD64 value × 0.5 + qSOFA score × 1.5). Multivariable logistic regression was used to assess independent predictive value. Diagnostic performance was analyzed using receiver operating characteristic (ROC) curves, and 28-day and 90-day survival outcomes were evaluated using Cox proportional hazards models. Results The sepsis group had significantly higher nCD64 index (2.10 ± 1.85 vs. 0.50 ± 0.60) and qSOFA scores (1.8 ± 0.8 vs. 0.7 ± 0.6) compared to the non-sepsis group (P < 0.001). Multivariable analysis identified nCD64 (OR 1.854, 95% CI 1.117–3.074, P = 0.017) and qSOFA (OR 9.303, 95% CI 3.513–24.658, P < 0.001) as independent predictors of sepsis. The combined index yielded an AUC of 0.94 (95% CI 0.90–0.97), with a sensitivity of 88.0% (83.5–92.5) and specificity of 91.0% (87.0–95.0), demonstrating superior diagnostic performance compared to nCD64 alone (AUC 0.91) or qSOFA alone (AUC 0.82). Elevated nCD64 was associated with increased 28-day and 90-day mortality (adjusted HR 2.15, 95% CI 1.32–3.50, P = 0.002). Conclusion The combination of nCD64 and qSOFA significantly improves the accuracy of early sepsis diagnosis and provides prognostic information. This composite tool is applicable in resource-limited settings and may help optimize clinical management and reduce the burden of sepsis.