Association between the systemic immune-inflammation index and prognosis in patients with stroke: a meta-analysis of cohort studies

Introduction The systemic immune-inflammation index (SII) is a newly recognized biomarker of inflammation. Although several studies have suggested that SII may aid in diagnosis of stroke and in predicting treatment outcomes, the findings remain inconsistent, and its relationship with clinical prognosis is still unclear. Therefore, we conducted a comprehensive systematic review and meta-analysis to explore the relationship between SII and clinical outcomes in patients with stroke. Methods We systematically searched four databases (PubMed, Embase, Cochrane Library, and Web of Science). The study adhered strictly to PRISMA guidelines. We assessed the risk of bias across the included studies using the Newcastle–Ottawa Scale. Key outcome indicators included poor functional outcome (modified Rankin Scale, mRS ≥ 2), mortality, stroke severity (National Institutes of Health Stroke Scale, NIHSS >4), and intracranial hemorrhage. Results A total of 11 cohort studies comprising 24,922 patients with stroke were included. Our results demonstrated that elevated SII was strongly linked to increased mortality (OR = 1.58, 95% CI: 1.23–2.02; p = 0.0003) and poor functional outcome (mRS ≥ 2) (OR = 2.03, 95% CI: 1.63–2.52; p = 0.0001). However, elevated SII was not associated with NIHSS >4 (OR = 3.40, 95% CI: 2.02–5.71; p = 0.80), nor with intracranial hemorrhage (OR = 2.41, 95% CI: 1.59–3.66; p = 0.35). Conclusion SII appears to have potential value in predicting stroke prognosis and may help clinicians assess outcomes by calculating patients’ SII levels. Nevertheless, given the limitations of the available evidence, further research is needed to clarify its practical clinical utility. Larger samples and multicenter clinical trials are required to obtain more robust conclusion. Systematic review registration https://www.crd.york.ac.uk/PROSPERO/view/CRD420251163979 , identifier PROSPERO (CRD420251163979).