Patient-level analysis of five international cohorts further confirms the efficacy of aspirin for the primary prevention of thrombosis in patients with antiphospholipid antibodies.

We performed an individual patient meta-analysis to determine whether aspirin has a significant protective effect on the risk of first thrombosis among patients with antiphospholipid antibodies (aPL). Five international cohort studies with available individual patient-level data, reporting on primary prophylaxis with continuous treatment with low-dose aspirin in patients with aPL were included. The main outcome was the occurrence of a first thrombotic in patients with aPL treated with low-dose aspirin compared to those not treated with low-dose aspirin. Pooled Hazard Ratios (HRs) and 95%CIs were calculated using frailty models. We pooled data from 497 subjects and 79 first thrombotic events (3469 patient-years of follow-up). After adjustment on cardiovascular risk factors, aPL profiles, and treatment with hydroxychloroquine, the HR for the risk of a first thrombosis of any type in aPL carriers treated with low-dose aspirin versus those not treated with aspirin was 0.43 (95%CI 0.25-0.75). Subgroup analysis showed a protective effect of aspirin against arterial (HR: 0.43 [95%CI: 0.20-0.93]) but not venous (HR: 0.49 [95%CI: 0.22-1.11]) thrombosis. Subgroup analysis according to underlying disease revealed a protective effect of aspirin against arterial thrombosis for systemic lupus erythematosus (SLE) (HR: 0.43 [95%CI: 0.20-0.94]) and asymptomatic aPL carriers (HR: 0.43 [95%CI 0.20-0.93]). We found no independent protective effect of hydroxychloroquine. This individual patient data meta-analysis shows that the risk of first thrombotic event as well of first arterial thrombotic event is significantly decreased among SLE patients and asymptomatic aPL individuals treated by low-dose aspirin.