Diagnostic utility of the modified inflammatory burden index and PCT/LYM ratio for sepsis stratification and early prediction of septic shock

Objective This study aimed to investigate the diagnostic performance of a modified inflammatory burden index (mIBI) and conventional biomarkers in sepsis and septic shock and assess the clinical utility of their combined application with the PCT/LYM ratio. Methods A retrospective analysis included 45 patients with sepsis, 77 with septic shock, and 54 with non-septic infectious inflammation (control). Levels of procalcitonin (PCT), C-reactive protein (CRP), interleukin-6 (IL-6), neutrophil count (NEU), and lymphocyte count (LYM) were measured. Composite indices including mIBI, PCT/LYM, CRP/LYM, and NLR were calculated. Multivariable logistic regression evaluated the independent diagnostic value of mIBI and PCT/LYM after adjusting for confounders. Results Inflammatory markers and composite indices increased progressively from control to sepsis to septic shock, whereas LYM decreased (all P < 0.05). For sepsis diagnosis, PCT/LYM showed strong diagnostic performance (AUC = 0.851, 95% CI: 0.775–0.928; sensitivity 80.00%, specificity 81.48% at cutoff 0.91), followed by mIBI (AUC = 0.806, specificity 88.89%). For septic shock, PCT/LYM (AUC = 0.880) and mIBI (AUC = 0.877) were comparable to PCT and IL-6 (all AUC = 0.879). Multivariable analysis revealed that after adjustment for age, sex, qSOFA, diabetes, and renal insufficiency, both log 10 (mIBI) (OR = 2.771, P < 0.001) and PCT/LYM (OR = 1.045, P = 0.002) were independent predictors for sepsis. For septic shock, log 10 (mIBI) retained independent predictive capacity (OR = 1.399, P = 0.030), whereas PCT/LYM showed a borderline association (OR = 1.004, P = 0.053). Conclusion The composite framework integrating PCT/LYM and mIBI addresses limitations of single biomarkers. PCT/LYM demonstrated independent predictive value, with a numerically higher AUC than PCT alone for both sepsis and septic shock, although the direct DeLong comparison did not reach statistical significance, supporting its potential utility as part of a composite screening approach. Modified IBI showed strong independent diagnostic value for sepsis and high univariate discriminative ability for septic shock. These routinely available indicators offer timely, cost-effective advantages for early sepsis identification and risk stratification.