Positive and strongly-positive results for IgG and IgM phospholipid (cardiolipin) antibodies (>40 GPL and/or >40 MPL) are diagnostic criteria for antiphospholipid syndrome (APS). Lesser levels of IgG and IgM phospholipid (cardiolipin) antibodies and antibodies of the IgA isotype may occur in patients with clinical signs of APS but the results are not considered diagnostic. Phospholipid (cardiolipin) antibodies must be detected on 2 or more occasions at least 12 weeks apart to fulfill the laboratory diagnostic criteria for APS. An IgA phospholipid (cardiolipin) antibody result above 15 APL with negative IgG and IgM phospholipids (cardiolipin) antibody results is not diagnostic for APS.

These infection-induced antibodies are usually transient and are not associated with an increased risk of clinical complications. In general, all patients who test positive for Anticardiolipin antibodies should be retested after six to eight weeks to rule out transient antibodies that are usually of no clinical significance.

- Individuals with the antiphospholipid antibody syndrome (APS) have an increased risk for stroke, myocardial infarction, venous thrombosis, thromboembolism, thrombocytopenia, and/or recurrent miscarriages. 

- 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.

- Anticardiolipin antibodies are often present in individuals with the antiphospholipid antibody syndrome.

- Anticardiolipin antibodies can often be observed during the convalescent phase of acute bacterial and viral infections and in individuals with syphilis. 

- Anticardiolipin antibodies are frequently observed in patients with other autoimmune disorders and malignancies. Individuals with Anticardiolipin antibodies secondary to these other conditions are at increased risk of developing APS. A variety of therapeutic drugs can induce the production of Anticardiolipin antibodies. These drug-induced antibodies may be clinically significant if they persist. Anti-cardiolipin antibodies are by definition a major criterion for a diagnosis of APS. They are found in around 30-40% of patients with SLE (=Systemic lupus erythematosus). In both patients with primary and SLE associated APS positive results correlate with a predisposition for arterial or venous thrombosis, foetal loss, or thrombocytopenia. However, levels of anticardiolipin antibodies do not correlate well with disease activity or with specific features of SLE such as arthritis or renal involvement. Nevertheless, the presence of these autoantibodies serves as a marker for the risk of a thromboembolic event. Those SLE patients exhibiting high levels of these autoantibodies are 4 times more likely to have such an event than those not expressing the autoantibodies. Anti-cardiolipin antibodies are associated with recurrent spontaneous abortion and with thrombotic events in mothers shortly after birth. They are also found in up to 20% of young stroke patients. Anti-phospholipid antibodies are also found in infections including syphilis, malaria, parasitic diseases and infectious mononucleosis. Indeed, anticardiolipin antibodies can be transiently elevated in many infections. For this reason, positive results should always be confirmed after 8 -12 weeks.