The presence of IgG antibodies against β2-glycoprotein I predicts the risk of thrombosis in patients with the lupus anticoagulant

Background: Lupus anticoagulant (LA) is a strong risk factor of thrombosis. However, a subgroup of patients positive for LA is unaffected by thrombosis and currently no predictive markers are available to identify patients positive for LA at increased risk for thrombosis. Objective: The aim of the study was to investigate whether anti-beta-2-glycoprotein I (anti-beta 2GPI) or anticardiolipin antibodies (ACA) are associated with an increased risk of thrombosis in patients persistently positive for LA. Patients and methods: A cohort of 87 consecutive patients persistently positive for LA was investigated, 55 with and 32 without a history of thrombosis. Immunoglobulin G (IgG) and M (IgM) antibodies against beta 2GPI and cardiolipin were determined by enzyme-linked immunoassay. Results: Patients positive for LA with thrombosis had significantly higher levels of anti-beta 2GPI IgG (median 16.7 standard units, interquartile range 3.0-75.2, P = 0.002) and of ACA IgG (41.1 IgG phospholipid units per mL, 8.9-109.0, P = 0.002) than those without thrombosis (2.6, 1.4-7.9 and 9.7, 4.6-22.1, respectively). Levels of anti-beta 2GPI IgM and ACA IgM did not differ significantly between LA patients with and without thrombosis (P = 0.25 and 0.12, respectively). Elevated anti-beta 2GPI IgG was associated with an increased risk for thrombosis (OR = 4.0, 95% CI 1.2-13.1), especially for venous thromboembolism (OR = 5.2, 95% CI 1.5-18.0). Conclusions: Increased levels of anti-beta 2GPI IgG were associated with thrombosis. We conclude that anti-beta 2GPI IgG levels above normal predict an increased risk of thrombosis in patients persistently positive for LA.