Antiphosphatidylserine/prothrombin antibodies in primary antiphospholipid syndrome

Antiprothrombin (aPT) antibodies may be detected by an enzyme-linked immunosorbent assay (ELISA) using a purified antigen or a phosphatidylserine/prothrombin complex (aPS/PT). IgG/IgM antibodies directed against aPS/PT were assessed in 158 patients with primary antiphospholipid syndrome (PAPS). They were detected in 80/158 (50.6%) PAPS patients; IgG alone was positive in 12 (7.6%), IgM alone in 36 (22.8%), and both IgG and IgM isotypes in 32 (20.2%) PAPS patients. IgG and IgM aPS/PT were significantly associated with both vascular thrombosis and pregnancy morbidity. IgG aPS/PT was significantly associated with venous thrombosis (p = 0.023), whilst IgG and IgM aPS/PT were associated with arterial thrombosis (p < 0.001 and p < 0.001, respectively). Logistic regression analysis showed that IgM and IgG aPS/PT were independent risk factors for thrombosis (odds ratio (OR) 3.5 [95% confidence interval (CI) 1.6-7.9] and OR 4.1 [95% CI 1.4-11.7], respectively) and IgM aPS/PT was an independent risk factor for arterial thrombosis (OR 2.7 [95% CI 1.1-6.7]). In conclusion, these findings indicate that aPS/PT are clinically relevant in PAPS.