The antiphospholipid and thrombosis syndromes.

Anticardiolipin antibodies and the lupus anticoagulant are strongly associated with thrombosis and appear to be the most common of the acquired blood protein defects causing thrombosis. Although the precise mechanism(s) whereby antiphospholipid antibodies alter hemostasis to induce a hypercoagulable state remain unclear, several theories have been advanced. The commonest thrombotic events associated with anticardiolipin antibodies are deep vein thrombosis and pulmonary embolus (type I syndrome), coronary or peripheral artery thrombosis (type II syndrome), or cerebrovascular/retinal vessel thrombosis (type III syndrome), and occasionally patients present with mixtures (type IV syndrome). The relative frequency of anticardiolipin antibodies in association with arterial and venous thrombosis strongly suggests that these should be looked for in any individual with unexplained thrombosis; all three idiotypes (IgG, IgA, and IgM) should be assessed. Also, the type of syndrome (I through IV) should be defined if possible because this may dictate both type and duration of immediate and long-term anticoagulant therapy. In contrast to those with anticardiolipin antibodies, patients with primary lupus anticoagulant thrombosis syndrome usually suffer venous thrombosis. Because the aPTT is unreliable in patients with lupus anticoagulant (prolonged in only about 40% to 50% of patients) and is not usually prolonged in patients with anticardiolipin antibodies, definitive tests (ELISA for anticardiolipin antibody and the dRVVT for lupus anticoagulant) should be immediately ordered when suspecting antiphospholipid syndrome or in individuals with otherwise unexplained thrombotic or thromboembolic events.