Antiphospholipid antibodies (aPL) are major risk factors for thrombosis. Other clinical factors exist in antiphospholipid syndrome (APS) patients which may have an additive or preventive effect on thrombosis. We therefore performed a cross-sectional study to analyse additive clinical thrombotic risk factors and possible preventive treatments in APS patients, and to compare the results with those obtained in asymptomatic aPL-positive (no history of vascular thrombosis or pregnancy morbidity) patients.

We identified 77 APS patients with non-gravid thrombotic events (group A) and 56 asymptomatic aPL-positive patients (group B). The study periods were defined as 6 months prior to the time of first vascular event in group A and 6 months prior to the patient's last visit in group B. Medical records were reviewed to evaluate the incidence of hypertension, diabetes mellitus, hypercholesterolaemia, regular cigarette smoking, oral contraceptive use or hormone replacement therapy, surgical procedures, pregnancy with or without an APS-related event, malignancy and infections. In addition, any history of thrombocytopenia or the use of aspirin, hydroxychloroquine, corticosteroids or immunosuppressives during the study periods was recorded. Bivariate statistical analysis and logistic regression tests were performed to compare groups.

In group A, 75% (n=58) of patients and in group B 48% (n=27) of patients had at least one of the additional risk factors during the study periods. In the bivariate analysis, pregnancy (P=0.005) and surgical procedures (P=0.04) were significantly more frequent in group A, while aspirin (P<0.001), hydroxychloroquine (P<0.001) and corticosteroids (P=0.002) were used significantly more frequently in group B. In logistic regression, the probability of an event was decreased by taking aspirin and/or hydroxychloroquine. In women only, the probability of an event was increased with thrombocytopenia and pregnancy or surgical procedures. The incidences of hypertension and smoking and the presence of more than one risk factor were significantly associated with arterial thrombosis but not venous thrombosis.

While traditional risk factors were similar between groups, pregnancy and surgical procedures increased the risk of thrombosis. Hypertension and smoking were associated with arterial events. Possessing a combination of risk factors may increase the occurrence of arterial thrombosis but not venous thrombosis. Use of aspirin and/or hydroxychloroquine may be protective against thrombosis in asymptomatic aPL-positive individuals.