Anti-cardiolipin

Anti-cardiolipin antibodies are one of three classic antiphospholipid antibodies (along with lupus anticoagulant and anti-β2-glycoprotein I antibodies) found in antiphospholipid syndrome (APS). APS can be primary or secondary (most commonly associated with SLE). Pathophysiology involves antibodies binding to phospholipid-binding plasma proteins (like β2-glycoprotein I) on cell surfaces, promoting a prothrombotic state through endothelial activation, platelet activation, and interference with natural anticoagulants (protein C, annexin A5). Clinically, APS presents with recurrent arterial and venous thromboses (DVT, PE, stroke), recurrent miscarriages (especially after 10 weeks gestation), livedo reticularis, and thrombocytopenia. Diagnosis requires both clinical criteria (thrombosis or pregnancy morbidity) and laboratory criteria (positive anticardiolipin antibodies, lupus anticoagulant, or anti-β2-glycoprotein I antibodies on two occasions at least 12 weeks apart). A key board-relevant point is that despite being prothrombotic in vivo, these antibodies cause a paradoxically prolonged PTT in vitro because they interfere with phospholipid-dependent coagulation assays — hence the term 'lupus anticoagulant' even though the patient is hypercoagulable, not anticoagulated. Anticardiolipin antibodies also cross-react with the antigen used in VDRL/RPR syphilis screening tests, leading to false-positive results — a classic association tested in SLE patients. Management includes long-term anticoagulation with warfarin (target INR 2-3, or higher for recurrent events) for thrombotic events; DOACs are generally avoided due to inferior efficacy in APS. In pregnancy, low-molecular-weight heparin plus aspirin is used to prevent miscarriage.