Dynamic Changes of Neutrophil Nuclear Membrane CD63 as a Potential Biomarker for Early Adjunctive Diagnosis and Prognostic Evaluation of Sepsis in Critically Ill Patients: A Prospective Cohort Study

ABSTRACT Sepsis has high intensive care unit mortality because biomarkers for early reversible pathological events are lacking. Targeted nuclear degranulation, the rate‐limiting step in neutrophil extracellular trap formation, refers to azurophilic granule fusion with the nuclear membrane. As an exclusive granule membrane marker, CD63 enrichment in nuclear membranes directly reflects this early pathogenic process. We developed a flow cytometry assay to quantify nuclear membrane CD63 (nmCD63) and validated its clinical utility in a two‐center prospective cohort with strict independent external validation. Assay protocols, diagnostic cutoffs, and combined models were established for the derivation cohort ( n = 180) and applied without recalibration to the validation cohort ( n = 76) comprising 256 participants. nmCD63 levels increased progressively with disease severity. They differentiated non‐infectious systemic inflammation from non‐severe infections (area under the curve [AUC] = 0.794) and outperformed C‐reactive protein and procalcitonin levels. Combined with the Sequential Organ Failure Assessment score, nmCD63 achieved an AUC of 0.943 for identifying sepsis in patients with a confirmed infection. Dynamic nmCD63 shifts preceded changes in all conventional biomarkers, and 7‐day trajectories enabled reliable prognostic stratification. This study translates targeted nuclear degranulation as a practical biomarker with dual diagnostic and prognostic value for sepsis in critically ill patients.