Neutrophil-derived ROS as a rapid functional biomarker: diagnostic and prognostic performance of the Leukocyte ImmunoTest in infection and sepsis

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Background: Early diagnosis of sepsis remains a major clinical challenge due to the dynamic interplay between infection and host immune response. Conventional biomarkers often fail to capture the dynamic nature of immune activation. Neutrophil-derived reactive oxygen species (ROS), central to antimicrobial defense and tissue injury, may offer early insight into immune dysregulation. The Leukocyte ImmunoTest (LIT) is a rapid, bedside assay that quantifies neutrophil ROS production within minutes, providing a functional snapshot of innate immunity. Methods: into three groups: inpatient controls (n=29), infection (n=47), and sepsis (n=106). LIT was performed on whole blood samples, expressed as relative light units (RLU), and compared with C-reactive protein (CRP), procalcitonin (PCT), white blood cell count (WBC), and neutrophil count (PMNL). Diagnostic performance was evaluated using receiver operating characteristic (ROC) analysis, and longitudinal LIT trends were assessed in relation to survival. Results: Median LIT values increased across diagnostic groups: 470 RLU in controls, 882 in infection, and 2466 in sepsis (adjusted p < 0.05). LIT demonstrated good diagnostic performance in identifying infection (AUC: 0.94, 95% CI: 0.911-0.968) and sepsis (AUC: 0.86, 95% CI: 0.795-0.915), with performance comparable to CRP and PCT, respectively. In a joint model, higher LIT values were independently associated with increased mortality (HR:1.6, 95% CI:1.2-2.2; p=0.005). Conclusion: LIT is a rapid bedside immune assay capturing the dynamic nature of neutrophil activation, demonstrating diagnostic and prognostic performance comparable to established biomarkers such as CRP and PCT in infection and sepsis. These findings suggest that LIT may have potential as a complementary biomarker in sepsis management. Multicenter studies are needed to confirm its integration into sepsis protocols and to further clarify its role in early recognition, risk stratification, and individualized care.

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