Lupus anticoagulant is an immunoglobulin that binds to phospholipids and proteins associated with the cell membrane. Its name is a misnomer, as it is actually a prothrombotic antibody. Lupus anticoagulant in living systems cause an increase in inappropriate blood clotting. The name derives from their properties in vitro, as these antibodies increase laboratory coagulation tests such as the activated partial thromboplastin time (aPTT). Investigators speculate that the antibodies interfere with phospholipids used to induce in vitro coagulation. In vivo, the antibodies are thought to interact with platelet membrane phospholipids, increasing adhesion and aggregation of platelets, which accounts for the in vivo prothrombotic characteristics.