ABO blood group in primary antiphospholipid syndrome: influence in the site of thrombosis?

Antiphospholipid syndrome (APS) is characterized by vascular thrombosis and/or obstetric complications associated with presence of antiphospholipid antibodies (aPL) but additional factors would also induce thrombosis. ABO (H) blood groups are known to be closely related to thrombosis, especially non-O blood type with venous events. The aim of this study was to investigate possible role of ABO (H) blood types in the thrombotic events in primary APS (PAPS). Seventy PAPS patients were selected for the study and were divided according to ABO blood group in: O PAPS (n = 26) and non-O PAPS (n = 44). ABO blood group phenotyping was performed by indirect technique. aPL anticardiolipin (aCL) and anti-βeta2 glycoprotein-1 (aβ2GPI) and the concentrations and activities of von Willebrand factor (VWF) were measured with ELISA. Lupus anticoagulant (LA) was detected by coagulation assays. A significant higher frequency of venous events was observed in non-O PAPS group (72.7 vs. 46.2 %, p = 0.040). In contrast, the frequency of arterial events was significantly higher in the O PAPS compared to the non-O PAPS group (69.2 vs. 36.4 %, respectively; p = 0.013). Frequencies of aCL, LA, aβ2GPI and triple aPL positivity were similar in both groups (p > 0.05). VWF antigen (75.54 ± 8.68 vs. 79.51 ± 7.07 IU/dl, p = 0.041) and activity (70.23 ± 11.96 vs. 77.92 ± 13.67 %, p = 0.020) were decreased in O PAPS compared to non-O blood group. VWF:CB/VWF:Ag ratio was similar among groups (p > 0.05). This is the first report that confirms the role of ABO blood system in thrombosis of PAPS and suggests that non-O blood group was related with venous events and O blood group with arterial thrombosis.