Background Persistently positive antiphospholipid antibodies (aPLs) are associated with an increased risk of arterial and venous thrombotic events (VTE). The pathogenesis of thrombosis is multifactorial and non-aPL thrombosis risk factors including hypertension (HTN), obesity, smoking, and diabetes (DM) influence the risk of thrombosis.1 ABO blood group, a determinant of plasma levels of von Willebrand factor (vWF), is an established thrombosis risk factor in the general population; non-type O blood type is associated with a higher risk of VTE. It is not known whether non-O blood type is associated with VTE in patients with persistent aPLs.
Objectives To investigate the association of ABO blood type with VTE in patients with persistent aPLs.
Methods We included patients >18 years old followed at an urban tertiary care center between 2000 and 2015 with the serologic criteria for aPL positivity by the revised Sapporo Criteria (anticardiolipin IgG or IgM >40 IU, and/or anti-beta-2-glycoprotein1 IgG or IgM >40 IU or LAC+ measured twice at least 12 weeks apart) and a type and screen.2 VTEs were verified through chart review by radiological criteria and historical records. Data including age, sex, race, body mass index, smoking status, blood type, HTN or DM diagnoses, and ever use of aspirin or warfarin were ascertained from chart review. Odds ratios of VTE were estimated with logistic regression models for O vs. non-O blood type.
Results Of the 230 patients included in the study, 48 (21%) were men, 78 (19 men, 59 women) had a VTE. Patients with and without VTE were similar with respect to age, sex, race, HTN, DM, and other clinical risk factors for VTE. The prevalence of non-O blood type was 46% in non-VTE and 56% in VTE, unadjusted OR 1.5 (95% CI 0.88, 2.62), p=0.14. However, among men, the prevalence of non-O was significantly higher in VTE than in non-VTE, 68% and 34%, respectively, p=0.021. Men with non-O blood type had higher odds of developing VTE, OR 4.0 (95% CI 1.1, 14.0), p=0.04 after adjusting for age, race, and DM and HTN. The association between ABO and VTE was not significant among women. In the overall sample, women were slightly younger at the time of aPL measurement, and were less likely to smoke, but more likely to have low density lipoprotein levels ≥100 mg/dl (Table 1). aPL positive women who developed VTE were more likely to be Hispanic compared to men with VTE, 54% and 25%, respectively, p=0.03, and were less likely to smoke compared to men.
Conclusions In this retrospective study, we have shown that the association between ABO and VTE varies by sex in aPL+ individuals. The non-O blood type is associated with a higher risk of VTE in men, but not women. The effects of ABO blood types on vWF in aPL+ individuals may be attenuated by genetic and environmental factors that differ by sex. Understanding the relationship between sex, ABO, and aPL may elucidate thrombosis mechanisms of VTE in aPL+ individuals.
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Disclosure of Interest None declared