Antibody profiles comprising anti phosphatidylserine/prothrombin differently affect thrombin generation and protein C resistance in antiphospholipid antibody carriers.

Anti phosphatidylserine/prothrombin antibodies (aPS/PT) are currently not included in the laboratory work-up of antiphospholipid symdrome (APS). However, several studies indicate that aPS/PT confer additional risk for thromboembolic events when added to classical antiphospholipid (aPL) antibody panel. We aimed to study thrombin generation (TG), a test that describes hyper or hypo-coagulability, in a cohort of antiphospholipid antibody (aPL) carriers with or without aPS/PT. As oral anticoagulants interfere with TG, we performed the study in carriers of aPL antibodies not on oral anticoagulants treatment. TG in tissue factor-triggered platelet-poor plasma and its inhibition by thrombomodulin was measured with a calibrated automated thrombogram method. Data are expressed as minutes (Interquartile Range). Of 55 aPL carriers, 37 were positive and 18 were negative for aPS/PT. Lag Time 5.4 min (4.1; 7.3) vs 3.4 min (3.0;4.5) is significant longer (p < 0.0001) and time to peak 9.6 min (8.1;11) vs 7.7 min (6.8;8.8) is significantly delayed (p = 0.0011) in aPS/PT positive as compared to aPS/PT negative carriers. Endogenous Thrombin Potential (ETP), peak thrombin formation and the velocity index are lower in aPS/PT positive carriers but did not reach statistical significance. Inhibition of ETP by thrombomodulin was significantly lower (protein C resistance) in aPS/PT positive vs aPS/PT negative group (22.8%±11.5 vs 34.9%±20.4, p = 0.01). In conclusion, aPS/PT positive carriers show an anticoagulant effect in TG while they exert a procoagulant effect in response to thrombomodulin-activated protein C.