Impact of ABO Blood Group on Vascular Complications and on Clinical and Functional Outcome After Aneurysmal Subarachnoid Hemorrhage.

Objective: To evaluate whether ABO blood group is associated with venous thromboembolic events (VTEs), cerebral severe vasospasm (CSV), delayed cerebral ischemia (DCI), and clinical or cognitive outcomes after aneurysmal subarachnoid hemorrhage (aSAH). Materials and Methods: A retrospective observational two-center cohort study of collected registry data, including 169 patients treated between September 2021 and November 2025. Outcomes were compared across ABO subtypes using univariate testing and multivariable logistic regression. Results: No ABO subtype was independently associated with VTE (7.7%), CSV/DCI (21.9%), intracranial hemorrhage, or in-hospital mortality (all p > 0.05). Higher age (OR 1.08, 95% CI 1.031-1.144, p = 0.003) was independently associated with increased in-hospital mortality, whereas single peri-interventional antiplatelet therapy (PIAT) (OR 0.076, 95% CI 0.004-0.506, p = 0.029) was associated with lower in-hospital mortality. ABO blood group was not associated with functional outcome (mRS) or cognitive performance (MoCA) in this cohort. Conclusions: In this two-center retrospective cohort, no independent association between ABO blood group and early cerebrovascular complications, functional outcome, or cognitive outcome after aSAH was detected. These findings suggest that short-term prognosis may be more strongly influenced by established patient- and treatment-related factors, particularly age and single PIAT. Further studies with larger cohorts are warranted to clarify the potential effect of ABO blood group on outcomes after aSAH.