Antiphospholipid Syndrome and Lupus Anticoagulant

In antiphospholipid antibody syndrome (APS), the body produces antibodies against a phospholipid, a cell membrane substance. This is referred to as an autoimmune disorder because the body produces antibodies against its own cells. Antiphospholipid antibody syndrome is characterized by antibodies against cardiolipin and β2 glycoprotein I.

Originally, it was thought that lupus anticoagulants were associated with bleeding, as they prolong clot-based tests such as the aPTT assay; however, they were later found to be associated with clotting. The development of a lupus anticoagulant may be temporary, particularly in children who have had a recent infection.

In patients with a lupus anticoagulant, 70% of the clotting events occur in the veins (venous clots), and the remaining 30% events occur in the arteries (arterial clots). The most common site for arterial clotting events is the blood vessels of the brain. These clotting episodes may be temporary or permanent and can often recur.


The Sapporo Antiphospholipid Antibody Syndrome Classification Criteria are used to diagnose antiphospholipid antibody syndrome.

The criteria include various clinical and laboratory abnormalities, such as:

  • Presence of blood clots in any organ or tissue,

  • Occurrence of one or more miscarriages or premature births,

  • Persistently positive results with a lupus anticoagulant test,

  • Moderate to high titer anticardiolipin antibodies, or

  • Moderate to high titer β2-glycoprotein-I antibodies

Antiphospholipid antibody syndrome can increase the risk of clotting in several ways, such as:

  • Promoting platelets to clump together

  • Reducing the production of activated protein C (a natural anticoagulant)

  • Blocking the anticoagulant activity of antithrombin, another naturally occurring anticoagulant


Catastrophic antiphospholipid antibody syndrome is a rapidly developing form of antiphospholipid antibody syndrome that results in multisystem organ failure. Although catastrophic antiphospholipid antibody syndrome occurs in less than 1% of all patients with antiphospholipid antibody syndrome, it is usually a life-threatening medical situation that requires a high degree of clinical awareness. The International Consensus Statement is commonly used for a definitive diagnosis of catastrophic antiphospholipid antibody syndrome.