Evaluating the efficacy of flow cytometry-derived sepsis index in the diagnosis of neonatal sepsis: a prospective observational study

Sepsis remains a major cause of neonatal morbidity and mortality worldwide, and early diagnosis continues to be challenging because of nonspecific clinical manifestations. Neutrophil CD64 (nCD64) upregulation and monocyte HLA-DR (mHLA-DR) downregulation are important immunological responses during sepsis. A flow cytometry-based Sepsis Index (SI), integrating nCD64 and mHLA-DR expression, may improve diagnostic accuracy compared with individual biomarkers. Hence, the study was done to determine the diagnostic accuracy of the Sepsis Index compared with individual biomarkers (nCD64 and mHLA-DR) in suspected neonatal sepsis. This prospective observational diagnostic accuracy study enrolled 81 neonates (41 suspected sepsis, 40 controls) at IMS & SUM Hospital, Bhubaneswar, India. Flow cytometry was used to measure nCD64 and mHLA-DR expression. ROC analysis determined optimal cut-offs. Sensitivity, specificity, predictive values, and likelihood ratios were calculated using SPSS v22. The mean fluorescence intensity (MFI) of nCD64 demonstrated a sensitivity of 43.90% and specificity of 74.36%, while mHLA-DR showed a sensitivity and specificity of 46.34% and 72.97%, respectively. The Sepsis Index exhibited superior diagnostic performance compared with either biomarker alone, achieving a sensitivity of 60.00%, specificity of 97.30%, PPV of 96.00%, NPV of 69.23%, and an AUC of 0.80. These findings indicate that the composite index provides improved discrimination between septic and non-septic neonates. The Sepsis Index is a sensitive and highly specific biomarker for diagnosing neonatal sepsis. Combining measures of neutrophil activation and monocyte immunosuppression provides a comprehensive assessment of immune dysregulation and yields higher diagnostic accuracy than either nCD64 or mHLA-DR alone. The Sepsis Index may serve as a valuable adjunctive tool for the early identification of neonatal sepsis and could help improve clinical decision-making in neonatal intensive care settings. Not applicable.