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Antiphospholipid Antibody Syndrome

Antiphospholipid antibodies (APLA) are a family of autoantibodies that recognize various combinations of phospholipids, phospholipid-binding proteins or both. These antibodies include lupus anticoagulants, detected by coagulation assays, and anticardiolipin antibodies (ACA), detected by immunoassays. Despite frequent concordance between these types of antibodies, they are not identical. The antiphospholipid antibody syndrome (APS) refers to the clinical association between these antibodies and a syndrome of hypercoagulability. The syndrome may be “primary”, in patients without another autoimmune disease, or “secondary”, associated with an autoimmune disorder, especially systemic lupus erythematosus. Diagnosis of this syndrome can be challenging, as APLA are relatively common among healthy control subjects (1-5% prevalence for both ACA and lupus anticoagulants), and this prevalence increases with advancing age. Clinically insignificant APLA may occur in association with other conditions such as infections or drug use. Correct diagnosis of APS has important implications regarding the use, choice and duration of anticoagulant therapy.

An international consensus statement was recently issued revising and updating the criteria for diagnosis of APS (J Thromb Haemost 2006; 4:295-306). The major changes/additions included in the new criteria are:

  • Inclusion of anti-beta-2-glycoprotein I (anti-B2GPI) as an additional laboratory criterion. One of the protein targets of APLA is beta-2-glycoprotein I, and antibodies against this protein are known to be closely related to clinical manifestations of APS.
  • Increase in the interval required to demonstrate persistence of the antibodies from 6 weeks to 12 weeks. This provides greater reassurance that the laboratory findings are clinically relevant, and not transient epiphenomena.
  • A diagnosis of APS should not be made if a period of greater than 5 years separates the clinical event and positive laboratory test.

According to the revised recommendations, APS is present if at least one of the following clinical criteria and one of the following laboratory criteria are met. Please note that the threshold values listed for ACA and anti-B2GPI must be determined by each laboratory .

Clinical Criteria:

  1. Vascular thrombosis- arterial, venous or small vessel, in any tissue or organ, confirmed by objective validated criteria
  2. Pregnancy morbidity
    1. Unexplained fetal death at or beyond 10 weeks gestation
    2. Premature birth before 34 weeks gestation because of eclampsia, severe pre-eclampsia or placental insufficiency
    3. Three or more unexplained consecutive spontaneous abortions before 10 weeks gestation

Laboratory Criteria:

  1. Lupus anticoagulant, present on at least 2 occasions, at least 12 weeks apart.
  2. Anticardiolipin antibodies (ACA), IgG or IgM, >30 units for both, present on at least 2 occasions, at least 12 weeks apart.
  3. Anti-beta–2-glycoprotein I antibodies (anti-B2GPI), IgG or IgM, >20 units for both,present on at least 2 occasions, at least 12 weeks apart.
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