ABO blood groups and hemorrhagic stroke: no overall association but ethnicity-specific protective effects

Background The ABO blood group system influences hemostatic factors, including von Willebrand factor and factor VIII, and has been implicated in thrombotic disorders. However, its role in hemorrhagic stroke remains uncertain. Objective To systematically evaluate the association between ABO blood groups and the risk of hemorrhagic stroke. Methods A comprehensive literature search of Scopus, WOSCC, China National Knowledge Infrastructure, and KoreaMed was conducted in accordance with PRISMA 2020 guidelines. Eligible case-control studies were included, and study quality was assessed using the Newcastle-Ottawa Scale. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated using meta-analytic techniques. Results Eleven studies comprising 6749 cases and 237,930 controls were included. No significant association was observed between ABO blood group and hemorrhagic stroke risk in the overall population. However, subgroup analyses identified modest but significant protective effects for blood group B in Asian populations (OR 0.93, 95% CI 0.88-0.99), and blood group AB in Caucasian populations (OR 0.64, 95% CI 0.44-0.93). Conclusions ABO blood groups are not major determinants of hemorrhagic stroke risk overall. Nonetheless, population-specific protective associations suggest that ABO-related hemostatic variation may contribute to ethnic differences in susceptibility. These findings highlight the importance of considering population heterogeneity and warrant further investigation in prospective studies.