ABO blood type and stroke risk: the REasons for Geographic And Racial Differences in Stroke Study.
BACKGROUND
ABO blood type is an inherited trait associated with coagulation factor levels and vascular outcomes.


OBJECTIVE
To assess the association of blood type with stroke and whether blood type contributes to racial disparities in stroke in the United States.


METHODS
The REasons for Geographic And Racial Differences in Stroke (REGARDS) Study recruited 30 239 participants between 2003 and 2007. Using a case-cohort design, blood type was genotyped in 646 participants with stroke and a 1104-participant cohort random sample. Cox models that adjusted for Framingham stroke risk factors were used to assess the association of blood type with stroke.


RESULTS
During 5.8 years of follow-up, blood types A or B vs. type O were not associated with stroke. Blood type AB vs. O was associated with an increased risk of stroke (adjusted hazard ratio [HR] 1.83, 95% confidence interval [CI] 1.01-3.30). The association of blood type AB vs. O was greater in those without diabetes (adjusted HR 3.33, 95% CI 1.61-6.88) than those with diabetes (adjusted HR 0.49, 95% CI 0.17-1.44) (P interaction = 0.02). Factor VIII levels accounted for 60% (95% CI 11%-98%) of the association of AB blood type and stroke risk.


CONCLUSIONS
Blood type AB is associated with an increased risk of stroke that is not attenuated by conventional stroke risk factors, and factor VIII levels were associated with 60% of the association. While blood type AB is rare in the US population, it is a significant stroke risk factor and may play an important role in stroke risk in these individuals.
University of Vermont College of Medicine, Burlington, VT, USA.
N A
NA
Zakai
S E
SE
Judd
K
K
Alexander
L A
LA
McClure
B M
BM
Kissela
G
G
Howard
M
M
Cushman
D000017:ABO Blood-Group System; D001741:Black or African American; D000368:Aged; D001779:Blood Coagulation Factors / Q000378:metabolism; D015331:Cohort Studies; D048909:Diabetes Complications / Q000097:blood; D005006:Ethnicity; D005260:Female; D005500:Follow-Up Studies; D005843:Geography; D006239:Haplotypes; D006801:Humans; D008297:Male; D008875:Middle Aged; D020641:Polymorphism, Single Nucleotide; D012307:Risk Factors; D020521:Stroke / Q000097:blood* / Q000175:diagnosis* / Q000208:ethnology; D016896:Treatment Outcome; D014481:United States; D044465:White People
D000017:ABO Blood-Group System; D001779:Blood Coagulation Factors
ABO blood-group system; continental population groups; factor VIII; risk factors; stroke