Antiphospholipid antibodies and thrombosis: strength of association.

Antiphospholipid antibodies, that is, lupus anticoagulants and anticardiolipin antibodies, are associated with thrombosis and obstetric complications in the antiphospholipid syndrome. Venous thrombosis occurs mostly in the lower limbs, with or without pulmonary embolism, and cerebral ischemia and transient ischemic attacks are the most common arterial events. Overall, the prevalence of thrombosis is about 30%, the rate of first event approximates 1%/year, and that of recurrence of patients not receiving anticoagulation is about 10-29%/year. The presence of lupus anticoagulants carries an odds ratio for thrombosis ranging from 5 to 16, and that of anticardiolipin antibodies from nonsignificant to 18. The detection of anti-beta2-glycoprotein I, but not antiprothrombin, antibodies might also help to identify antiphospholipid-positive patients at risk of thrombosis. Unfractionated or low-molecular-weight heparin followed by oral anticoagulation represents the current treatment of both arterial and venous thrombosis. However, uncertainty still exists about the optimal duration and intensity of oral anticoagulation following the first event. Several therapeutic clinical trials are currently being conducted, which soon clarify these issues. The prevalence of obstetric complications is about 15-20%. The presence of lupus anticoagulants carries an odds ratio for recurrent miscarriages and fetal death ranging from 3.0 to 4.8, whereas that of anticardiolipin antibodies goes from 0.86 to 20. Unfractionated or low-molecular-weight heparin in combination with low-dose aspirin represents the current standard of treatment of pregnant antiphospholipid-positive women to prevent recurrent obstetric complications. Upon treatment, the live birth rate increases from 0-40% to 70-80%.