Antiphospholipid antibodies

Antiphospholipid antibodies (APAs) are a heterogenous group of antibodies directed against plasma proteins which bind to phospholipids.

• seen in 1-5% of apparently healthy subjects
• increased prevalence is seen with age and may be influenced by chronic disease, infections, malignancies and certain drugs
• it can arise as a primary phenomenon or secondary to other disorders such as connective tissue disorders, infections and malignancy (2)
• types of antiphospholipid antibodies include
  • lupus anticoagulant
    • the specificity for thrombosis is higher for LA than aCL or anti–β2-glycoprotein I antibodies (anti- β2GPI)
    • also it is greater for higher than lower titre aCL
  • anti–β2-glycoprotein I antibodies (anti- β2GPI)
  • anticardiolipin antibodies (1)
• appropriate laboratory tests considered for detection of APAs include:
  • lupus-anticoagulant assays -
    • a functional assay based on a combination of several clotting tests
    • detects immunoglobulins that cause prolonged clotting times in vitro but are associated with thrombosis in vivo
    • some commonly used tests are the activated partial thromboplastin time (aPTT), the dilute Russell's viper venom time (dRVVT), and the kaolin clotting time (KCT).
  • cardiolipin ELISA - detects antibodies against cardiolipin and cardiolipin bound β2-glycoprotein I
  • anti– β2-glycoprotein I ELISA - antibodies against β2-glycoprotein I
• in patients who have all three tests positive, there is a higher risk for pregnancy morbidity or thromboembolism

Reference:

• (1) Cohen D et al. Diagnosis and management of the antiphospholipid syndrome. BMJ. 2010;340:c2541
• (2) Giannakopoulos B, Krilis SA.The pathogenesis of the antiphospholipid syndrome. N Engl J Med. 2013;368(11):1033-44
• (3) Keeling D et al.Guidelines on the investigation and management of antiphospholipid syndrome. Br J Haematol. 2012;157(1):47-58.