Efficacy of aspirin for the primary prevention of thrombosis in patients with antiphospholipid antibodies: an international and collaborative meta-analysis.

We performed a meta-analysis to determine whether aspirin has a significant protective effect on risk of first thrombosis among patients with antiphospholipid antibodies (aPL+). Observational and interventional studies identified from the Medline, Embase and Cochrane databases were selected if they assessed the incidence of first thrombosis in aPL+ patients treated with aspirin versus those without. Pooled effect estimates were obtained using a random-effects model. Of 1211 citation retrieved, 11 primary studies (10 observational and 1 interventional) met inclusion criteria, including a total of 1208 patients and 139 thrombotic events. The pooled odds ratio (OR) for the risk of first thrombosis in patients treated with aspirin (n=601) was 0.50 (95%CI: 0.27 to 0.93) compared to those without aspirin (n=607), with significant heterogeneity across studies (I(2)=46%, p=0.05). Subgroup analysis showed a protective effect of aspirin against arterial (OR: 0.48 [95%CI: 0.28-0.82]) but not venous (OR: 0.58 [95% CI: 0.32-1.06]) thrombosis, as well as in retrospective (OR: 0.23 [0.13-0.42]) but not prospective studies (OR: 0.91 [0.52-1.59]). Subgroup analysis according to underlying disease revealed a significant protective effect of aspirin for asymptomatic aPL+ individuals (OR: 0.50 [0.25-0.99]), for systemic lupus erythematosus (SLE) (OR: 0.55 [0.31-0.98]) and obstetrical antiphospholipid syndrome (APS) (OR: 0.25 [0.10-0.62]). This meta-analysis shows that the risk of first thrombotic event is significantly decreased by low dose aspirin among asymptomatic aPL individuals, patients with SLE or obstetrical APS. Importantly, no significant risk reduction was observed when considering only prospective studies or those with the best methodological quality.