Lupus anticoagulant

The expected result is Not detected; a positive result is confirmed by repeating the test at least twelve weeks later, because temporary positives are common after infections.

Despite its name, a lupus anticoagulant is an antibody that makes clotting tests take longer in the test tube while making clots more likely, not less, in the body. It is one of the antiphospholipid antibodies. The test is a set of clotting assays, usually including the dilute Russell viper venom time, from which the laboratory reports whether the antibody is present.

Doctors request it when someone has had an unexplained blood clot, particularly at a young age or in an unusual place, after recurrent miscarriage, when the APTT is unexpectedly long, and in people with lupus or related autoimmune conditions.

• Antiphospholipid syndrome, an autoimmune clotting condition
• Systemic lupus erythematosus and related autoimmune conditions
• Recent infections, which commonly cause a temporary positive
• Some medicines, including some antibiotics and antipsychotics
• Some cancers

• A negative result means the antibody was not found; it does not exclude other antiphospholipid antibodies, which are measured separately

• A temporary positive after an infection is common and disappears on repeat testing
• Anticoagulant medicines, including warfarin, heparin and the direct oral anticoagulants, interfere with the test and can give false positives; laboratories ask that it be done off these where possible
• An under-filled or delayed citrate tube can produce a misleading result

No fasting needed. Best taken when well, off anticoagulant medicines where the doctor agrees, and repeated after twelve weeks if positive.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.