Comparison of SOFA score alone versus SOFA score with interleukin-6 for outcome prediction in ICU patients with sepsis: a prospective observational study

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Background Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection, with high global morbidity and mortality. The Sepsis-3 definition endorses the Sequential Organ Failure Assessment (SOFA) score to quantify organ dysfunction, though it was not originally designed for prognostication. Biomarkers such as interleukin-6 (IL-6), a key pro-inflammatory cytokine, have shown promise in reflecting disease severity and rising earlier than clinical scores. Aim This study aimed to compare the SOFA score with the SOFA score and interleukin-6 level in the accurate prediction of outcome as a survivor or non-survivor at the end of 15 days among patients admitted to the ICU in a tertiary care hospital. Methods This prospective observational study was conducted in a tertiary care ICU. In total, 40 adult patients (18–50 years) with sepsis (Sepsis-3 criteria) and an anticipated ICU stay of >72 h were enrolled. Patients with acute coronary syndrome, terminal malignancy, major burns, elective postoperative ventilation, COVID-19, or inter-ICU transfer were excluded. SOFA scores and serum IL-6 levels were measured at admission (Day 0) and at 24-h intervals up to 72 h (Days 1–3). Patients were followed for 15 days and classified as survivors or non-survivors. The prognostic performance of SOFA, IL-6, and the combined score was assessed using receiver operating characteristic (ROC) analysis. Internal validation was performed using bootstrap resampling with 1,000 iterations to obtain optimism-corrected area under the curve (AUC) values. Results Of the 40 patients, 24 (60%) survived, and 16 (40%) died within 15 days. Non-survivors had significantly higher SOFA scores at admission compared with survivors [median of 13 (IQR 10–15) vs. 10 (IQR 8–12); p = 0.006]. Survivors demonstrated a declining SOFA score trend over time, while non-survivors showed progressive increases ( p < 0.05 at all timepoints). IL-6 levels were consistently higher in non-survivors across Days 0–3 ( p < 0.05). Discriminative performance improved over time for both SOFA and IL-6, with the highest AUCs on Day 3 (SOFA: 0.986; IL-6: 0.993). After bootstrap internal validation, the optimism-corrected AUC for the combined SOFA–IL-6 score on Day 3 was 0.908 (95% CI: 0.824–0.992), comparable to SOFA alone (corrected AUC 0.908, 95% CI: 0.826–0.990). On Days 0–2, the combined score showed modestly higher corrected AUCs compared to SOFA alone (improvements of +0.024 to +0.048). Conclusion In this hypothesis-generating study, combining the SOFA score with IL-6 showed modest improvements on Days 0–2 compared with SOFA alone. On Day 3, both scores performed equivalently. This integrated approach may provide a practical and dynamic tool for early prognostication in critically ill patients with sepsis.