Antibody detection against β2 glycoprotein 1 is used in the investigation of patients with antiphospholipid syndrome.
Β2 glycoprotein 1 (β2-GP1, also called apolipoprotein H) is a 326 amino acid polypeptide composed of hepatocytes, endothelial cells and trophoblast cells. Β2-GP1 and phospholipid complexes in vivo present epitopes that react with native autoantibodies. In the blood of normal individuals there may be low concentrations of IgG autoantibodies against β2-GP1 that react with moderate affinity.
Abnormal levels of antibodies against β2-GP1 are present in patients with antiphospholipid syndrome (APS). Patients with antiphospholipid syndrome may develop a variety of clinical symptoms, including thrombosis, pregnancy complications, unexplained skin disorders (reticular pellucida, gangrene pyoderma), thrombocytopenia. Antibodies against β2-GP1 have been found to be increased in patients with systemic autoimmune diseases such as systemic lupus erythematosus.
Antibodies against β2-GP1 can be measured in the laboratory by different types of tests, including immunological tests and functional coagulation tests. Immunological tests for antibodies against β2-GP1 can be performed using either a complex substrate consisting of β2-GP1 together with anionic phospholipids (e.g. cardiolipin or phosphatidylserine) or β2-GP1 alone. Antibodies detected by immunological tests using complex substrates are commonly referred to as anti-phospholipid or cardiolipin antibodies. Antibodies detected using β2-GP1 alone without phospholipids are referred to as "antibodies against β2-GP1". Some antibodies against β2-GP1 are capable of inhibiting clot formation in functional coagulation assays containing low concentrations of phospholipid cofactors. Antibodies detected by functional coagulation assays are commonly referred to as lupus anticoagulant.
The diagnosis of antiphospholipid syndrome requires that at least 1 clinical and 1 laboratory criterion be met. Clinical criteria include vascular thrombosis (arterial or venous in any organ or tissue) and pregnancy complications (unexplained fetal death, premature birth, severe preeclampsia or placental insufficiency). Other clinical manifestations that are often associated with the syndrome, including heart valve disease, reticular pelletization, thrombocytopenia, nephropathy, neurological symptoms, are not included in the diagnostic criteria. Laboratory criteria for the diagnosis of antiphospholipid syndrome are the presence of anticoagulant lupus, the presence of IgG and / or IgM cardiolipin antibodies, and the presence of IgG and / or IgM antibodies against β2-GP1. All antibodies should be screened for 2 or more times at least 12 weeks apart. Antibodies against β2-GP1 are somewhat more specific (but less sensitive) for the diagnosis of antiphospholipid syndrome. Antibodies against cardiolipin and to β2-GP1 of the IgA class are not part of the laboratory criteria because of their low specificity.
Possible Interpretations of Pathological Values
- Increase: Anti-phospholipid syndrome, systemic lupus erythematosus, thrombosis, thrombocytopenia, recurrent miscarriage, syphilis, acute infection, elderly. False-positive results have been observed in patients taking medications such as chlorpromazine, hydralazine, penicillin, phenytoin, procaineamide, quinidine.
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. Correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
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