Immune-inflammatory indices and a serum surrogate composite score of blood–brain barrier injury in acute ischemic stroke

Background Systemic inflammation is linked to blood–brain barrier (BBB) breakdown in acute ischemic stroke (AIS), but the association between peripheral immune-inflammatory indices and BBB permeability remains unclear.Methods We enrolled 286 AIS patients within 24 h of onset. Five indices (NLR, PLR, LMR, SII, SIRI) were calculated from admission samples. A serum surrogate score integrating MMP-9, S100B, and BDNF (not calibrated against DCE-MRI or CSF albumin quotient) indicated BBB injury.Results All five indices correlated significantly with the surrogate score after Bonferroni correction (all adjusted p < 0.01). In adjusted regression, SII (β = 0.452, p < 0.001) and NLR (β = 0.387, p < 0.001) were independent correlates. SII had the highest adjusted AUC (0.768; 95% CI 0.711–0.819), indicating moderate discrimination for high surrogate-defined BBB injury. The SII–score association was stronger in patients with NIHSS ≥ 8 (P~interaction~=0.024), with a similar non-significant trend for infarct volume ≥15 mL (P~interaction~=0.067). SII correlated positively with MMP-9 (r = 0.402, p < 0.001).Conclusions SII and NLR are independently associated with a serum surrogate score of BBB injury in AIS. SII shows moderate discrimination and may aid early risk stratification, pending validation against gold-standard measures. The SII–MMP-9 correlation suggests shared inflammatory pathways warranting further study.