RheumatologyTier 2Topic

Laboratory tests - anticardiolipin antibody

What it is

Anticardiolipin antibody - one of the three antiphospholipid antibodies used in APS diagnostic criteria, historically the first antiphospholipid antibody identified and still widely tested alongside anti-beta-2 glycoprotein I and lupus anticoagulant
Tested in the same clinical scenarios as the other antiphospholipid antibodies - unexplained thrombosis, recurrent pregnancy loss, SLE workup

Assay

Detected by ELISA against cardiolipin, a phospholipid; in practice most clinically significant anticardiolipin reactivity is now understood to be beta-2 glycoprotein I-dependent (the antibody actually recognises the protein-phospholipid complex, not cardiolipin alone) - explaining the substantial overlap with anti-beta-2 glycoprotein I positivity

Criteria and pitfalls

Same requirement as the other antiphospholipid antibodies: IgG or IgM at moderate-high titre, confirmed on two occasions at least 12 weeks apart
Low-titre or transient anticardiolipin positivity is common (e.g. post-infection) and not clinically significant - titre and persistence both matter for interpretation, not simply a positive/negative result

Management

Same management framework as the other antiphospholipid antibodies - confirmed APS warrants anticoagulation (thrombotic APS) or aspirin/heparin (obstetric APS during pregnancy); isolated antibody positivity without a qualifying clinical event does not by itself mandate treatment

Associations

Antiphospholipid syndrome, SLE, recurrent pregnancy loss, catastrophic APS (a rare, severe multi-organ thrombotic variant)

The three antibodies together

Anticardiolipin, anti-beta-2 glycoprotein I, and lupus anticoagulant should be interpreted together as a panel rather than in isolation - the number of positive tests ("single, double, or triple positivity") is itself prognostically important for thrombotic risk

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