Cardiolipin, IgG antibodies
Why this test?
For the diagnosis of antiphospholipid syndrome.
To assess the risk of developing venous and arterial thrombosis in patients with antiphospholipid syndrome.
In what cases is it prescribed?
In the presence of symptoms of venous or arterial thrombosis in a young (up to 50 years) patient or thrombosis of unusual localization.
When examining a patient with habitual miscarriage, that is, if a woman has a history of three or more spontaneous abortions in a row up to 22 weeks.
With other indirect signs of antiphospholipid syndrome: symptoms of heart valve damage (vegetation, thickening, dysfunction), reticular liver disease, nephropathy, thrombocytopenia, preeclampsia, chorea, epilepsy.
With thrombosis or pregnancy loss in patients with autoimmune diseases (for example, SLE).
Along with lupus anticoagulant when receiving an increased partial thromboplastin time (PTT).
With a positive result of the RPR test during syphilis screening.
Antibodies to cardiolipin (ACL) are autoantibodies produced against one of the phospholipids of the mitochondrial membrane - cardiolipin. Moreover, they are directed not against the phospholipid itself, but against the plasma apolipoprotein (beta-2-glycoprotein) associated with cardiolipin. ACLs belong to the group of antiphospholipid antibodies, which also includes lupus anticoagulant, antibodies to beta-2-glycoprotein, prothrombin, proteins C and S, and other antigens.
They have prothrombogenic potential, and their presence in the blood is associated with venous and arterial thrombosis and habitual miscarriage - the combination of these immunological and clinical signs is called antiphospholipid syndrome (APS).
Confirmation of the diagnosis of APS is based on the detection of antiphospholipid antibodies in the blood. More often than others, it is possible to determine ACS (which is why the syndrome is also called anticardiolipin syndrome). It is desirable that the study of ACL was carried out outside the episode of acute thrombosis.
This is due to the fact that against the background of current thrombosis, a transient appearance of ACL is possible, not related to the presence of antiphospholipid syndrome. For differential diagnosis of transient and persistent ACS production, the study is repeated after 12 weeks. Since the presence of ACL is not the only and not the main cause of venous and arterial thrombosis, the analysis is not indicated in all cases of thrombotic syndrome. It is considered inappropriate in the group of elderly patients with signs of thrombosis.
Conversely, the study is indicated for thrombosis in young patients (younger than 50 years) or thrombosis of unusual localization. The ACL test is characterized by high sensitivity, but its specificity is low. Patients with viral infections (herpes zoster, HIV), polymyalgia rheumatica, giant cell arteritis, epilepsy, chorea and some other conditions may have a positive test result. As a rule, the production of ACL in these diseases is a short-term and benign phenomenon, and when re-examined after 6-12 weeks, the result becomes negative (maintaining a positive result should alert the doctor about the presence of antiphospholipid syndrome). Detection of ACL is a necessary, but not sufficient, criterion for making a diagnosis of antiphospholipid syndrome. Other mandatory laboratory criteria include lupus anticoagulant and antibodies to beta-2-glycoprotein.
As a rule, it is possible to detect all three variants of antiphospholipid autoantibodies in the blood of patients with pronounced signs of APS. In addition, the presence of three variants of autoantibodies is associated with a high risk of thrombotic conditions in the future. If the diagnosis of antiphospholipid syndrome has been established, there is no need to periodically repeat the ACL study. Exceptions are cases when the clinical picture of the disease changes unpredictably and a reassessment of the diagnosis is required.
The result of the ACL study can change in the same patient over time, which, however, does not depend on the degree of disease activity and therefore is not used to control the treatment of APS. In the vast majority of cases, APS is diagnosed in patients with autoimmune diseases, most often - systemic lupus erythematosus (SLE). Such an APS is called secondary. Therefore, when examining patients with SLE, analysis for ACS and other antiphospholipid antibodies is necessary to rule out APS. Detection of ACL in patients without signs of any autoimmune disease is called primary APS. Primary and secondary APS have many common features, which does not always allow differentiating these conditions on the basis of the clinical picture.
However, differential diagnosis of variants of antiphospholipid syndrome is necessary for the interpretation of ACL research results. Thus, the positive predictive value (PPV) of detecting ACL in a patient at risk for antiphospholipid syndrome (for example, a patient with SLE) is higher than the PPV of detecting ACL in a patient without autoimmune diseases. Diagnosis of secondary APS has some features. The presence in the blood of patients with autoimmune diseases of other autoantibodies (primarily, rheumatoid factor, RF) can affect the results of the study. The presence of RF leads to an overestimation of the IgM-AKS titer and, as a result, may affect the result of the analysis as a whole.
Therefore, the interpretation of the results of the ACL study in such patients is carried out taking into account the data on the presence of RF. Patients with ACL in the blood serum demonstrate a positive result of the RPR test for syphilis, since in this study a complex of phospholipids, including cardiolipin, is used as an antigen. In such cases, for the correct interpretation of the RPR test result, a more specific study of ACL is performed.