Cardiolipin Antibodies, IgG and IgM

Cardiolipin Antibodies, IgG and IgM (anticardiolipin antibodies; aCL) testing supports the diagnosis and classification of antiphospholipid syndrome (APS). Results contribute to assessment of thrombotic risk in patients with suspected or established APS, encompassing both venous and arterial events. This assay is often interpreted alongside other antiphospholipid antibody studies, including lupus anticoagulant and anti–beta-2 glycoprotein I, to refine clinical risk estimation and guide management decisions.

Anticardiolipin antibodies (aCL) recognize complexes of cardiolipin with beta-2 glycoprotein I and are part of the antiphospholipid antibody spectrum, which also includes lupus anticoagulant and anti–beta-2 glycoprotein I. Their presence associates with venous and arterial thrombosis and with pregnancy morbidity in keeping with antiphospholipid syndrome (APS). Testing is best performed outside an acute thrombotic episode, as transient aCL reactivity can occur; persistence must be demonstrated by repeat testing after 12 weeks for APS classification. While aCL assays offer relatively high analytical sensitivity, clinical specificity is limited, and low-titer or short-lived positivity may accompany infections and other conditions. APS classification requires appropriate clinical manifestations together with persistent laboratory positivity, often with concordant lupus anticoagulant and anti–beta-2 glycoprotein I results; concurrent positivity for all three markers correlates with higher thrombotic risk. Once APS is established, routine serial aCL measurement is not recommended unless there is a change in clinical status. Rheumatoid factor may spuriously elevate IgM aCL values and should be considered during interpretation. Biologic false-positive nontreponemal syphilis tests (e.g., RPR) can arise because these assays use cardiolipin-containing antigens and warrant follow-up with specific antibody testing.