Thrombotic risk factors in primary antiphospholipid syndrome: a 5-year prospective study.

Background and Purpose: Because thromboembolic events are frequently observed in primary antiphospholipid syndrome (PAPS), we assessed the risk factors for new thrombotic episodes.
Methods: Fifty-six PAPS patients (mean age, 37+/-10 years) were prospectively studied for 5 years. The preliminary Sapporo classification criteria for antiphospholipid syndrome (APS; a medium-high anticardiolipin antibody [aCL] titer and/or a positive lupus anticoagulant [LA] test in the presence of vascular thrombosis and/or pregnancy morbidity) were used to confirm the diagnosis. Thrombotic episodes or pregnancy losses before a diagnosis of PAPS were considered events, and any new disease manifestation other than thrombocytopenia was considered a recurrent event. Only patients with objectively verified thrombotic events were included in the study.
Results: Twenty-one new thrombotic events were observed in 15 subjects (26.8%), including 3 (5.4%) who died during the follow-up. The patients with IgG aCL levels of >40 IgG phospholipid unit (GPL-U) showed a higher incidence of new thrombotic events (43.3%) than those with levels of < or =40 GPL-U (7.7%). Univariate analysis identified a history of recurrent clinical events (P=0.004), a highly positive aCL titer (P=0.007), and the presence of cardiac abnormalities (P=0.036) as significant risk factors for new thrombotic events. A multivariate regression model confirmed that an IgG aCL titer of >40 GPL-U was an independent risk factor for thrombosis (odds ratio, 9.17; 95% confidence interval, 1.83 to 46.05).
Conclusions: A high IgG aCL titer is the strongest predictor of new thrombotic events in PAPS patients.