Anti–β2-Glycoprotein I IgA Antibodies

Antiphospholipid syndrome (APS), also known as Hughes syndrome, is an autoimmune disease characterised by thrombophilia. Cumulative haematologic/clinical manifestations include venous thrombosis (37%) or arterial thrombosis (27–49%), cytopenia (30–38%), complications during pregnancy (55–74%), neurological (66%) and cardiac (27%) involvement, as well as pulmonary (20–30%) or cutaneous (40%) tissue damage due to the underlying circulatory disorders.

APS is classified as primary (pAPS) or secondary (sAPS). Both forms present the same type of immune and haematologic response; however, in sAPS this response is a secondary manifestation to another autoimmune disorder or a specific pathological condition.

A final diagnosis of APS requires at least one clinical criterion (thrombosis or complications during pregnancy) and one laboratory criterion (medium-to-high antibody titres in serum/plasma at an interval of at least 12 weeks).

Antibodies against β2-GP1 are specific markers for both pAPS and sAPS. The ACR/EULAR classification criteria for the diagnosis of APS include the serological determination of anti-β2-GP1 as a laboratory criterion. Anti-β2-GP1 testing is crucial to confirm suspected APS cases that are negative for anticardiolipin antibodies or lupus anticoagulant.

IgG and/or IgM antibodies against β2-GP1 are present in 30–80% of APS patients. In suspected APS with negative IgG/IgM anti-β2-GP1 and anticardiolipin, tests should be performed for the IgA isotype of both autoantibodies.