Impact of the systemic immune-inflammation index (sii) on prognosis in patients with chronic total occlusion (CTO): a systematic review and meta-analysis

Background Chronic total occlusion (CTO) carries high ischemic risk and variable procedural success. The systemic immune-inflammation index (SII), derived from platelet, neutrophil, and lymphocyte counts, reflects thrombo-inflammatory activity and may refine risk stratification in CTO. This meta-analysis evaluated the association between SII and CTO outcomes. Methods We systematically searched PubMed, Scopus, and Google Scholar through September 2025 in accordance with PRISMA. Six observational studies assessing SII and CTO outcomes (mortality, major adverse cardiovascular events [MACE], and coronary collateral circulation [CCC]) were included. Data on demographics, comorbidities, SII cut-offs, and outcomes were extracted. Random-effects models were used to pool area-under-the-curve (AUC) estimates. Heterogeneity was quantified with the I² statistic. Association effect sizes (adjusted odds ratios [ORs]) were summarized when pooling was not feasible because SII was reported on different scales (categorical vs continuous). Results Of 19 records identified, six studies comprising 4,182 patients (mean age- 62 years, mean follow up- 61 months) met inclusion criteria. Four studies reported the diagnostic performance of SII for poor CCC. The pooled AUC was 0.72 (95% CI 0.67–0.77, I² = 74%), indicating fair discrimination. Three studies linked higher SII with poor CCC, including one diabetic-CTO cohort with a strong adjusted association (adjusted OR 2.96, 95% CI 2.54–3.45, p < 0.001). For clinical outcomes, two CTO–percutaneous coronary intervention cohorts showed that higher SII independently predicted MACE (adjusted ORs 2.04, p = 0.02 and 3.32, p = 0.0001). One cohort reported that higher SII was independently associated with all-cause mortality in CTO patients (adjusted OR 2.82, 95% CI 1.03–7.75). Conclusions SII is a simple, low-cost biomarker which shows fair discriminatory ability for poor CCC and is consistently associated with adverse prognosis in CTO including higher MACE, poorer collateralization, and increased mortality. Additional prospective, multicenter validation with standardized cut-offs are needed to confirm its clinical significance and prognostic potential.