Systemic immune-inflammation index predicts hemorrhagic transformation after endovascular therapy for ischemic stroke

The systemic immune-inflammation index (SII) has emerged as a novel biomarker in vascular diseases. We investigated its association with hemorrhagic transformation after endovascular therapy (EVT), stress hyperglycemia ratio (SHR), early neurological deterioration (END), and long-term clinical outcomes in acute ischemic stroke. We screened consecutive ischemic stroke patients eligible for EVT between May 2014 and May 2025. Inclusion criteria were: (1) availability of admission SII, calculated as platelets×neutrophils/lymphocytes [10³/µL]; and (2) assessment of symptomatic intracerebral hemorrhage (ICH) after EVT, defined as an NIHSS score worsening ≥4. SHR was defined as admission glucose [mg/dL]/(28.7 × HbA1c [%]-46.7). END was defined as neurological worsening of NIHSS ≥ 2 within 72 h after admission. An unfavorable outcome was defined as an mRS score of 4-6 at 3 months. Of 336 screened patients, 317 (161 men; median age, 80 years) were included. Symptomatic ICH was observed in 30 (9%). Higher SII was significantly associated with symptomatic ICH across all multivariable models (p < 0.005). Higher SII was also associated with Safe Implementation of Treatments in Stroke-Monitoring Study (SITS-MOST)-defined parenchymal hematoma type 2 and type 1 at 24 h after EVT (p < 0.005). In addition, SII positively correlated with SHR (B 1090, 95% CI 636 - 1544, p < 0.001), and was associated with END (PR 1.119, 95% CI 1.002 - 1.249, p = 0.045) and unfavorable outcome (PR 1.119, 95% CI 1.029 - 1.217, p = 0.009). Elevated SII reflects acute immune-inflammatory imbalance and stress response in ischemic stroke undergoing EVT and may serve as a predictor of hemorrhagic complications and unfavorable outcomes.