To explore the effectiveness of Systemic-immune-inflammation-index scoring system in predicting the risk of cerebral vasospasm and delayed ischemia following aneurysmal subarachnoid-hemorrhage.

Systemic immune-inflammation index (SII), defined as neutrophils×platelets/lymphocytes, is an important tool for assessing the inflammatory status which has been recently investigated in a range of inflammatory conditions such as malignancies and cardiovascular and pulmonary pathologies. However, there remains a paucity of knowledge regarding its utility in predicting the risk of cerebral vasospasm (CVS) and delayed cerebral ischemia (DCI) after subarachnoid hemorrhage (aSAH).

• A systematic search from the literature was carried out to extract relevant studies. The primary outcomes of the study were incidence of CVS/DCI and functional outcomes. Poor functional outcome was defined as a modified Rankin scale (mRS) score ≥ 3.

• This updated systematic review included data from six studies with more than 1300 patients with aSAH. SII value was significantly associated with increased risk of CVS and DCI. SII was significantly higher in the DCI group than in the non-DCI group with an AUCs of 0.860 (95% CI: 0.818–0.896, p < 0.001) and 0.7 (95% CI: 0.60-0.80, p < 0.05). Similar correlation was found with CVS with AUCs of 0.666 (p < 0.05) and 0.767 (95% CI: 0.703–0.831, p < 0.001). SII was also significantly associated with worse long-term functional outcomes according to mRS (p = 0.040 and p < 0.05).

• SII is a practical clinical tool that can predict the risk of DCI and CVS in aSAH. The significant correlation between SII and poor functional outcomes suggests that it could serve as a valuable, non-invasive biomarker for early identification of high-risk patients, and guiding prevention and intervention strategies. This also sets the stage for large-scale multicenter studies to confirm its global applicability, which could significantly improve timely management decisions, particularly in limited-resource settings and high-burden setups.