Influence of antiphospholipid antibody levels and type on thrombotic manifestations: results from the Serbian National Cohort Study.

Repeated thromboses are the most frequent clinical manifestation of antiphospholipid syndrome (APS) in the presence of antiphospholipid antibodies (aPL). The objective of this study was to observe the prevalence and localization of thrombosis, and to investigate the importance of aPL type and level for thrombosis-related events in patients diagnosed with APS. These are the first results of patients enrolled in Serbian National Cohort Study which comprises 256 patients: 162 with primary antiphospholipid syndrome (PAPS) and 94 with APS associated with systemic lupus erythematosus (SLE). aPL analysis included detection of aCL (IgG/IgM), β(2)GPI, and lupus anticoagulant. Thrombosis was diagnosed in 119 (46.5%) patients, with higher prevalence in PAPS compared with SLE patients (51.2% and 38.3%, respectively, p = 0.045). There was similar prevalence of arterial thrombosis in PAPS and SLE groups (34.6% and 34%, respectively, p = 0.932) although venous thrombosis was more frequent in PAPS (25.9% and 8.5%, respectively, p = 0.001). Thrombosis was observed in 92 (55.8%) patients who had more than one type of antibody (category I), in 13 (41.9%) patients with category IIa, in 19 (46.3%) patients with category IIb, and in 73 (44.2%) patients with category IIc (p = 0.10). The patients with thrombosis were older than those without thrombosis (49.8 and 39.8 years, respectively, p = 0.001). Overall, older age was a risk factor for thrombosis. The prevalence of venous thrombosis was higher in the PAPS group, but with lower frequency than in literature data. Any aPL type and level is a risk factor for thrombosis.