The antiphospholipid and thrombosis (APL-T) syndromes. Clinical and laboratory correlates.

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 mechanisms by which antiphospholipid antibodies alter hemostasis to induce a hypercoagulable state remain unclear, several theories have been advanced. The most common thrombotic events associated with anticardiolipin antibodies are deep venous thrombosis and pulmonary embolus (type I syndrome), coronary or peripheral artery thrombosis (type II syndrome), or cerebrovascular-retinal vessel thrombosis (type III syndrome); 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 measured. Also, the type of syndrome (I through V) should be defined, if possible, as this may dictate both the type and duration of both immediate and long-term anticoagulant therapy. Unlike patients with anticardiolipin antibodies, patients with primary lupus anticoagulant thrombosis syndrome usually sustain venous thrombosis. Because the aPTT is unreliable in patients with lupus anticoagulant (prolonged in approximately 40% to 50% of patients) and is seldom prolonged in patients with anticardiolipin antibodies, definitive tests (ELISA for anticardiolipin antibodies and the dRVVT for lupus anticoagulant) should be immediately ordered when antiphospholipid syndrome is suspected or when individuals present with otherwise unexplained thrombotic or thromboembolic events.