Diagnostic Accuracy of the Systemic Immune-Inflammation Index and Procalcitonin in Patients with Sepsis at Adam Malik Hospital Medan

Abstract

Background: Early diagnosis of sepsis is essential to improve patient outcomes. Procalcitonin (PCT) is a widely used biomarker for sepsis but may be limited by its cost and availability. The Systemic Immune-Inflammation Index (SII), derived from routine hematological parameters, has been proposed as a simple and inexpensive alternative. This study aimed to compare the diagnostic accuracy of SII and PCT in patients with suspected sepsis.

Methods: A cross-sectional diagnostic accuracy study was conducted in the Emergency Department of H. Adam Malik General Hospital, Medan. Fifty-five patients with suspected infection were enrolled, including 32 patients with sepsis and 23 without sepsis based on the Sepsis-3 criteria. Diagnostic performance was evaluated using receiver operating characteristic (ROC) curve analysis, including the area under the curve (AUC), sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), Youden index, and comparison of AUCs using the DeLong test.

Results: The optimal cut-off value for SII was 1,752,635, with an AUC of 0.564 (95% CI: 0.42–0.69), sensitivity of 68.8%, and specificity of 56.5%. PCT demonstrated superior diagnostic performance, with an optimal cut-off value of 1.265 ng/mL, an AUC of 0.863 (95% CI: 0.74–0.94), sensitivity of 75.0%, and specificity of 82.6%. The difference in AUC between SII and PCT was statistically significant (p = 0.0007). The combined SII–PCT model yielded an AUC of 0.872.

Conclusion: Procalcitonin demonstrated significantly higher diagnostic accuracy than SII for identifying sepsis. The combined SII–PCT model showed good diagnostic performance and warrants further evaluation in larger studies.