Supplementary Material for: Role of the ABO blood groups as a risk factor for retinal vein occlusion

Introduction
A recent study suggested that non-O blood groups had an increased risk for the presence of RVO. In this study we investigated (i) an association between blood group and the presence of RVO and (ii) whether this association correlated to other RVO risk factors.

Methods
We included 485 RVO patients and 295 control subjects who were recruited in this case-control study. We determined ABO genotypes rs8176719 as a marker for the O allele and rs8176746 for the B allele by polymerase chain reaction.

Results
We did not find an association between ABO blood group and the presence of RVO. In detail, the proportion of ABO blood groups was similar among RVO patients and control subjects (p=0.527). In a logistic regression, non-O blood group was associated with 1.06-fold higher odds of being a RVO patient (95%CI: 0.78-1.45, p=0.693), and this lack of association prevailed upon multivariable adjustment for age, gender, history of stroke and venous thromboembolism and co-medication with lipid-lowering agents.

Discussion
Although non-O blood groups are a known risk factor for thrombotic and cardiovascular disease, they do not seem to be a major risk factor for the development of RVO.