Lupus anticoagulant
A confusingly named antibody: despite 'anticoagulant', it actually raises the risk of clotting in the body. It is one of the antibodies of antiphospholipid syndrome, tested after unexplained clots or recurrent miscarriage. The result is reported as present or absent, and needs confirmation on a repeat test.
What it measures
The lupus anticoagulant is a type of antiphospholipid antibody — an antibody directed against certain fats (phospholipids) and associated proteins involved in clotting. Its name is misleading in two ways: it is not confined to lupus (it occurs in people without it), and although it is called an 'anticoagulant' because it prolongs clotting tests in the laboratory test tube, in the body it paradoxically increases the tendency to form clots. It is detected through a sequence of clotting tests (a prolonged phospholipid-dependent clotting time that corrects when phospholipid is added back), reported qualitatively as present or absent. Along with two other antibodies (anticardiolipin and anti-beta-2-glycoprotein I), it is one of the markers of antiphospholipid syndrome — an autoimmune clotting disorder that causes venous and arterial clots (such as DVT, pulmonary embolism and stroke) and pregnancy complications including recurrent miscarriage. Because these antibodies can appear transiently after infection, a positive result must be confirmed on a repeat test at least 12 weeks later before it counts toward a diagnosis. It is tested after an unexplained or unusual clot, a clot at a young age, or recurrent pregnancy loss.
What a high value can mean
- Positive (present) — an antiphospholipid antibody is detected; must be confirmed on a repeat ≥12 weeks later.
- Antiphospholipid syndrome — when persistent and combined with clots or pregnancy loss.
- A clue after an unexplained clot or recurrent miscarriage — helps explain the clotting tendency.
- A transient positive after infection or with some medications — why confirmation is required.
What a low value can mean
- Absent (negative) — no lupus anticoagulant detected; the expected result in most people.
- A negative does not fully exclude antiphospholipid syndrome — the other antibodies (anticardiolipin, anti-beta-2-glycoprotein I) are tested too.
When to discuss with a doctor
The lupus anticoagulant is tested in specific situations — after an unexplained or unusual blood clot (a DVT, pulmonary embolism or stroke), a clot at a young age, or recurrent miscarriage or pregnancy complications — usually as part of an antiphospholipid antibody panel. A single positive result is not enough: because these antibodies can appear briefly after infection, it must be confirmed on a repeat at least 12 weeks later, and diagnosis of antiphospholipid syndrome requires both persistent antibodies and a clinical event. If confirmed, management (which may include blood thinners, and specific care in pregnancy) is directed by a haematologist or rheumatologist. Mediora.AI can surface a lupus anticoagulant result alongside the related clotting markers so the pattern is visible; confirming and interpreting it belongs with your specialist.