What is a Lupus Anticoagulant (LAC)?

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What is a Lupus Anticoagulant (LAC)?

A lupus anticoagulant (LAC) is a poorly-named phenomenon that is somewhat common in the coagulation lab. LAC refers to antibodies that patients develop that bind to phospholipids or phospholipid-binding proteins. These antibodies includes those that target:

  • Beta-2-glycoprotein 1
  • Phosphatidylserine, Phosphatidylcholine, Annexin
  • Cardiolipin
As you can probably infer, antibodies which bind these proteins can markedly interfere with common coagulation tests like the PT and aPTT. The term LAC was ascribed to this condition since these antibodies are associated with the autoimmune disease lupus. But most LAC antibodies are found in patients who do not have a diagnosis of lupus. Antibodies bound to cell membranes can induce clotting. Patients with LAC may develop antiphospholipid syndrome (APS) which has serious clinical implications that include high risk for stroke, heart attack, kidney damage, deep vein thrombosis, pulmonary embolism, preeclampsia and fetal loss. The term 'lupus anticoagulant' is thus confusing since these antibodies are not limited to lupus patients, nor are they 'anticoagulants' in vivo. These antibodies have the opposite effect, they increase the risk of thrombosis.
A diagnosis of APS requires the following:
  1. A clinical thrombotic event and
  2. The Presence of LAC or
  3. The presence of IgG or IgM anti-cardiolipin or beta-2-glycoprotein-1 antibodies that are found on 2 or more occasions separated by 12 weeks. (IgA antibodies are not included)