Anti–Cardiolipin IgM 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).

The ACR/EULAR classification criteria for APS include the serological determination of anti-cardiolipin antibodies (ACA) as a laboratory criterion. The prevalence of ACA is high, ranging between 60–90% (ACA IgG 44%, ACA IgM 12%, ACA IgG/IgM 88%) with persistence exceeding 12 weeks in APS patients. ACAs are detected in 15–30% of sera from patients with sAPS, conferring high test sensitivity.

The specificity of ACA is limited; high titres may also occur in other autoimmune diseases, infectious conditions and following drug administration.

Persistently high ACA titres are considered a risk factor for thrombosis and vascular complications, including myocardial infarction or stroke, with an 80% probability of occurrence.