Lupus anticoagulant (also known as lupus antibody, LA, LAC, or lupus inhibitors) is an immunoglobulin that binds to phospholipids and proteins associated with the cell membrane. Lupus anticoagulant is a misnomer, as it is actually a prothrombotic agent. That is, Lupus anticoagulant antibodies in living systems cause an increase in inappropriate blood clotting. Their name derives from their properties in vitro, since in laboratory tests, these antibodies cause an increase in aPTT. It is speculated that the antibodies interfere with phospholipids utilized to induce in vitro coagulation. In vivo, it is thought to interact with platelet membrane phospholipids, increasing adhesion and aggregation of platelets; thus its in vivo prothrombotic characteristics.