Clinical Value of EMR3 in Sepsis Diagnosis, Monitoring, and Prognosis: A Multicenter Prospective Observational Study

Sepsis is a life-threatening condition caused by a dysregulated immune response to infection, leading to organ dysfunction and increased mortality. Early diagnosis and accurate assessment of disease progression remain challenging. EMR3 (ADGRE3), a receptor expressed on the surface of neutrophils, may serve as a potential biomarker for sepsis diagnosis, immune response monitoring, and prognosis assessment. However, its clinical value requires further validation in large, multicenter prospective studies. This multicenter, prospective, observational study will enroll approximately 3,000 adults across 8-15 hospitals in China. Participants will be classified into four groups: patients with sepsis or septic shock, patients with infection without sepsis, patients with noninfectious critical illnesses, and healthy or elective surgical controls. Neutrophil EMR3 expression will be measured using flow cytometry on residual blood samples obtained during routine clinical care. Patients with sepsis will undergo repeated measurements at baseline, 72 ± 12 hours, and day 7 ± 1 day, with an optional assessment at day 14 ± 2 days. Other participants will undergo baseline testing only. All participants will receive standard clinical care without study-related interventions or additional blood collection. The primary outcome is the diagnostic accuracy of baseline neutrophil EMR3 expression for identifying sepsis, assessed by the area under the receiver operating characteristic curve (AUC). Secondary outcomes include changes in EMR3 expression over time, associations with 28-day all-cause mortality, septic shock, organ dysfunction, secondary infections, and intensive care unit length of stay. The study will also compare EMR3 with established biomarkers, including CD64, HLA-DR, procalcitonin, C-reactive protein, and lactate, and evaluate whether incorporating EMR3 into combined models improves diagnostic and prognostic performance. This study aims to determine whether neutrophil EMR3 can serve as a reliable biomarker for early sepsis diagnosis, disease monitoring, and risk stratification.

\*\*Inclusion Criteria:\*\* * Age ≥18 years. * Patients admitted for the first time to the ICU or emergency ICU (EICU) of a participating center during the study period, including patients with suspected or confirmed infection, sepsis, septic shock, or noninfectious critical illness. Healthy volunteers undergoing routine health examinations may also be included as controls. * Availability of residual EDTA-anticoagulated whole blood from routine clinical testing at enrollment, suitable for flow cytometry within the predefined testing window. * Provision of written informed consent by the participant or a legally authorized representative, with an independent witness when required. * Ability to complete baseline clinical data collection and 28-day outcome follow-up, as determined by the investigator. * Expected survival of more than 72 hours. \*\*Exclusion Criteria:\*\* * Receipt of chemotherapy, chimeric antigen receptor T-cell (CAR-T) therapy, hematopoietic stem cell transplantation, or high-dose immunosuppressive therapy within 30 days before enrollment. Participants included in a predefined exploratory immunosuppression subgroup will be excluded from the primary diagnostic analysis. * Active hematological malignancy, severe granulocytopenia, or absolute neutrophil count \