Abstract
Background: Non-O blood type is associated with higher procoagulant proteins and potentially stroke. Prior studies may overestimate the association due to lack of control for race and stroke risk factors as there are known racial differences in blood type, conventional stroke risk factors, and stroke risk. Methods: REGARDS recruited 30,239 participants in their homes between 2003-07 from the continental US; 55% were female, 41% were black, and 56% lived in the southeast (by design). Using a case-cohort design, 553 participants with incident stroke and 991 participants without baseline stroke were genotyped to determine blood type. Cox proportional hazard models adjusting for race and Framingham or ARIC stroke risk factors were used to determine the association of blood type with incident stroke. Results: Blacks had a higher frequency of blood type B (17% vs. 10%) and AB (5% vs. 2%) and a lower frequency of blood type O (31% vs. 42%) than whites (p <0.001) (Table). Except for diabetes (OR 4.1 95% CI 2.1, 7.9) and higher systolic blood pressure (7.5 mm hg higher, p = 0.01) for blood type AB vs. O, stroke risk factors did not differ by blood type. Over 4.5 years of follow-up, neither blood types A or B were associated with incident stroke accounting for race and traditional stroke risk factors (Table). Blood type AB was associated with a marginally increased risk of stroke after adjusting for race and Framingham (HR 1.8; 95% CI 1.0, 3.4) or ARIC (HR 1.8; 95% CI 1.0, 3.3) stroke risk factors (Table). Discussion: Blood type AB is associated with an increased risk of stroke which is not mediated by conventional stroke risk factors. This association could relate to increased factor VIII or von Willebrand factor in individuals with non-O blood type but this does not explain the unique association of blood type AB with stroke. Whether blood type should be incorporated into clinical stroke risk models is unknown.
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