A cardiolipin antibodies test looks for a certain kind of antibody in your blood. An antibody is a substance in your blood that helps fight off infection. The antibodies attack cardiolipins by mistake. Cardiolipin is a phospholipid, or a kind of fat in the blood that is important for blood clotting. When the antibodies attack cardiolipin, blood clots can occur. Platelets, blood cells that help blood to clot, also get used up, leading to problems with bleeding. The levels of these antibodies are often high in people with abnormal blood clotting, autoimmune diseases like systemic lupus erythematosus (SLE), or repeated miscarriages.