Anticardiolipins are antibodies produced by the immune system against the platelet membrane phospholipids responsible for the coagulation of blood clots. Anticardiolipin antibodies are often responsible (with lupus anticoagulants and beta-2 glycoprotein antibodies) for the abnormal formation of clots in veins (phlebitis) and arteries (arterial thromboses). They are involved in antiphospholipid syndrome, which occurs, for example, through repeated miscarriages during the second or third trimester of pregnancy. There are three types of anticardiolipin antibodies: IgG, IgA and IgM. The test measures IgG and IgM levels.
A negative anticardiolipin IgG or IgM result indicates that this type of antibody was not present or was present in too small a quantity in the blood sample being tested. Slightly or moderately positive results are sometimes temporarily observed in older individuals with no symptoms following an infection or after taking a medication. These results are most often of little clinical significance but must be interpreted along with other clinical information. Moderately or very high levels of anticardiolipin antibodies that persist for 12 weeks or more indicate a continued presence of these autoantibodies and an increased risk of abnormal clots and miscarriages.