The association between ABO blood types and venous thromboembolism in individuals with a positive antiphospholipid profile is varied by sex.

Objectives Although non-O blood type is an established risk factor for venous thromboembolism in the general population, the impact of ABO blood type (ABO) on venous thromboembolism risk in individuals with persistent antiphospholipid antibodies (aPL) has not been studied. We sought to investigate the relationship between ABO and venous thromboembolism in aPL-positive individuals. We also sought to explore potential interactions between ABO and sex or race to determine whether ABO contributes to race or sex differences with respect to the development of venous thromboembolism. Methods We identified all patients over 18 years old followed at a tertiary medical center between January 2000 and January 2015 with serological aPL criteria and ABO data. Episodes of venous thromboembolism were recorded. Logistic regression models were fitted to estimate odds ratios (ORs) of venous thromboembolism for non-O (A, B, or AB blood types) versus O blood type. Results There were 226 patients included in the final analysis, of whom 75 (33%) had reported venous thromboembolism. In the overall sample, there was a non-significant difference between venous thromboembolism in patients with non-O blood type compared to O blood type (OR 1.64, 95% confidence interval (CI) 0.94, 2.88; P = 0.08). Men with non-O blood type had a significantly higher risk of venous thromboembolism as compared to men with O-type blood (OR 4.94, 95% CI 1.37, 17.85; P = 0.02), but there was no significant association between ABO and venous thromboembolism among women (OR 0.96, 95% CI 0.50, 1.83; P = 0.52). Conclusions Non-O blood type may be an under-recognized risk factor for venous thromboembolism among men with persistent aPL antibodies, whereas the risk associated with non-O blood type seen in the general population may be attenuated in aPL-positive women.