Anticardiolipin antibody
One of the antiphospholipid antibodies — autoantibodies linked to an increased tendency to form blood clots and to pregnancy complications. A persistently positive result, especially after a clot or recurrent miscarriage, is part of diagnosing antiphospholipid syndrome.
What it measures
Anticardiolipin antibody is one of the three main antiphospholipid antibodies (alongside lupus anticoagulant and anti-beta-2-glycoprotein I) — autoantibodies directed against phospholipids and associated proteins on cell membranes. Rather than measuring an infection or a nutrient, it identifies an autoimmune tendency to abnormal blood clotting. Its significance is its link to the antiphospholipid syndrome: a condition in which these antibodies drive an increased risk of blood clots in veins or arteries (such as deep vein thrombosis, stroke or clots in the placenta) and of pregnancy complications, particularly recurrent miscarriage and stillbirth. Both IgG and IgM classes are usually measured. A key principle is that the result must be persistent: a single positive test can occur transiently after infections or with certain medications and is not enough to diagnose the syndrome, so a positive result is repeated after at least 12 weeks to confirm it is durable. The syndrome can occur on its own (primary) or alongside another autoimmune disease, especially lupus (secondary). Diagnosis combines a persistently positive antibody with a clinical event — a clot or a defined pregnancy complication — and is made by a specialist, because it carries important implications for anticoagulation and for managing pregnancy.
What a high value can mean
- Antiphospholipid syndrome — the key association, especially when persistently positive with a clot or pregnancy complication.
- An increased tendency to blood clots — in veins or arteries (e.g. deep vein thrombosis, stroke).
- Recurrent miscarriage or other pregnancy complications — a defining clinical feature.
- Often found with lupus — the syndrome can be secondary to another autoimmune disease.
- A transient positive — can follow infections or some medications; needs repeat testing to confirm.
What a low value can mean
- Negative — the expected result; makes anticardiolipin-associated antiphospholipid syndrome unlikely.
- A single positive that later turns negative — was likely transient, not the syndrome; confirmation requires persistence.
When to discuss with a doctor
Anticardiolipin antibody is tested when antiphospholipid syndrome is suspected — for example after an unexplained blood clot, a stroke at a young age, recurrent miscarriage or stillbirth, or in someone with lupus. Because a single positive can be transient, a positive result is confirmed by repeating it after at least 12 weeks; a persistently positive result together with a clinical event points to the syndrome, which is diagnosed and managed by a specialist. This matters because it influences important decisions about blood-thinning treatment and the management of pregnancy. A positive result on its own, without a clinical event, is not the same as having the syndrome and needs careful interpretation. Mediora.AI can surface a positive anticardiolipin antibody so the clotting-risk pattern is visible in your results, but confirming the diagnosis and deciding on any treatment belongs with your doctor and specialist.