IgG phosphatidylserine/prothrombin antibodies as a risk factor of thrombosis in antiphospholipid antibody carriers

The clinical significance of IgG/IgM antiphosphatidylserine/prothrombin (aPS/PT) antibodies was prospectively evaluated in a cohort of 191 antiphospholipid antibody (aPL) carriers using commercial ELISA assays. IgG aPS/PT antibodies were detected in 40 (20.9%) and IgM aPS/PT in 102 (53.4%) of the carriers. Both IgG and IgM aPS/PT antibodies were significantly associated with triple aPL positivity (Lupus anticoagulants [LAC] plus anti-beta 2Glycoprotein I plus anticardiolipin antibodies) (p = 0.0000 for both). There was a significant prevalence of IgM aPS/PT in the individuals with isolated LAC positivity (p = 0.005). Fourteen of the aPL carriers (7.3%) developed a first thrombotic event. There was a significant prevalence of IgG aPS/PT antibodies but not of IgM aPS/PT in the thrombotic patients (p = 0.015). The cumulative incidence rate of thrombotic events was significantly higher in the IgG aPS/PT positive (p = 0.035) but not in the IgM aPS/PT positive carriers. Logistic regression analysis assessing the independent effect of IgG/IgM aPS/PT antibodies, triple aPL positivity, genetic/acquired thrombosis risk factors and autoimmune disorders on thrombosis development uncovered a significant association only for the risk factors (Odds Ratio = OR: 12.451, 95% Confidence Interval = CI: 2.519-61.537, p = 0.002) and for triple aPL positivity (OR: 4.725, 95% CI: 1.135-19.674, p = 0.033). Logistic regression evaluating the independent effect of IgG and IgM aPS/PT on thrombosis development uncovered a significant association only for the former (OR: 3.962, 95% CI: 1.174-13.37, p = 0.026). The risk score for thrombosis in aPL carriers could be more effective if IgG aPS/PT antibodies are added to triple aPL positivity and thrombosis risk factors.