Cardiolipin Antibodies, IgG and IgM

Cardiolipin Antibodies, IgG and IgM is used alongside lupus anticoagulant and anti–beta-2 glycoprotein I to evaluate suspected antiphospholipid syndrome (APS). The assay, commonly referred to as anticardiolipin antibodies (aCL), helps assess risk for venous or arterial thrombosis and for pregnancy morbidity in patients under consideration for APS, including those with autoimmune conditions such as systemic lupus erythematosus. Incorporating this antiphospholipid antibody measurement into the diagnostic workup improves characterization of thrombotic risk and obstetric complications when APS is in the differential diagnosis.

Anticardiolipin antibodies are part of the antiphospholipid antibody family and recognize beta-2 glycoprotein I when complexed with cardiolipin. Their presence is associated with venous and arterial thrombosis and adverse pregnancy outcomes; when these clinical events occur together with laboratory evidence of antiphospholipid antibodies, the condition is termed antiphospholipid syndrome (APS). Testing is best performed outside an acute thrombotic episode because aCL can be transient; to confirm persistence, repeat testing after 12 weeks is recommended. aCL assays generally show higher analytical sensitivity but lower specificity, as temporary positivity may accompany infections and other conditions; persistent reactivity raises concern for APS. aCL alone do not establish APS classification; laboratory criteria also include lupus anticoagulant and anti–beta-2 glycoprotein I, and triple positivity is linked to higher prospective thrombotic risk. Serial measurement is not useful for treatment monitoring because titers may vary independently of disease activity; retesting is reserved for substantial changes in clinical status. Rheumatoid factor can artifactually elevate IgM aCL results and should be considered during interpretation. aCL positivity may produce false-positive nontreponemal syphilis screens (RPR), necessitating confirmatory testing.