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Antiphospholipid syndrome
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Antiphospholipid syndrome

Antiphospholipid syndrome is an autoimmune disorder that causes an increased tendency to form abnormal blood clots, which can lead to serious complications like stroke or pregnancy loss.

Overview

Antiphospholipid syndrome is a disorder characterized by an increased tendency to form abnormal blood clots, known as thrombophilia. These clots can block blood vessels throughout the body. If a clot forms in the brain, it can lead to a stroke. As an autoimmune disorder, it occurs when the immune system attacks the body's own tissues and organs.

Symptoms

Symptoms often appear in early to mid-adulthood and may include:

  • Blood and Vessel Issues: Reduced platelets (thrombocytopenia), a shortage of red blood cells due to premature breakdown (hemolysis), and purplish skin discoloration (livedo reticularis).
  • Skin and Neurological: Open sores (ulcers) on the skin and migraine headaches.
  • Pregnancy Complications: Increased risk of preeclampsia, placental insufficiency, early delivery, or miscarriage.
  • Catastrophic Antiphospholipid Syndrome (CAPS): A rare, life-threatening form where clots form in multiple vessels simultaneously, leading to organ failure.

Causes

The condition results from the presence of three abnormal immune proteins in the blood, known as antiphospholipid antibodies: lupus anticoagulant, anticardiolipin, and anti-B2 glycoprotein I. These antibodies attack normal human proteins, causing them to change shape and activate the blood clotting pathway. While the exact genetic cause is unknown, the production of these antibodies may be triggered by exposure to foreign invaders like viruses or bacteria that mimic human proteins.

Inheritance

Most cases are sporadic, occurring in people with no family history of the disorder. While it rarely runs in families, there is no clear pattern of inheritance, suggesting that multiple genetic and environmental factors contribute to the risk.

Frequently Asked Questions

CAPS is a rare, life-threatening manifestation where microvascular thrombosis rapidly develops across multiple organ systems over days to weeks. Common triggers include invasive surgical procedures, severe infections, sudden withdrawal of anticoagulation, trauma, or active cancer. Critical warning signs include sudden breathlessness (pulmonary embolism or acute respiratory distress syndrome), acute kidney dysfunction (decreased urine output and rising blood pressure), altered mental state or encephalopathy, skin necrosis, and sudden multi-organ failure. Immediate treatment requires a combination of therapeutic anticoagulation, high-dose corticosteroids, plasma exchange, and intravenous immunoglobulins (IVIG).
Major clinical trials have demonstrated that direct oral anticoagulants (such as rivaroxaban and apixaban) are associated with a significantly higher rate of recurrent arterial thrombosis (like strokes) and venous thromboembolism compared to standard vitamin K antagonists in high-risk APS patients, particularly those who are "triple positive" (testing positive for all three antibody types). Therefore, dose-adjusted warfarin with a target international normalized ratio (INR), typically maintained between 2.0 and 3.0, remains the gold-standard oral anticoagulant for long-term thrombosis prevention in APS.
Diagnosis requires meeting at least one clinical criterion (an objectively documented vascular thrombosis or specific pregnancy complications, such as recurrent early miscarriages or late-term fetal loss) alongside persistent laboratory evidence. Laboratory criteria require positive testing for lupus anticoagulant, anticardiolipin antibodies (IgG or IgM), or anti-beta-2-glycoprotein I antibodies (IgG or IgM). Crucially, the antibody test must remain positive on two or more occasions drawn at least 12 weeks apart, because transient antiphospholipid antibodies can appear temporarily following common viral infections without indicating true autoimmune disease.
Management during pregnancy centers on preventing placental thrombosis and fetal loss while minimizing maternal clotting risks. Standard therapy involves combining low-dose aspirin (initiated preconception or early in the first trimester) with prophylactic or therapeutic doses of low-molecular-weight heparin (LMWH) starting upon confirmation of pregnancy. Because warfarin is teratogenic, women on long-term warfarin must switch to LMWH before or immediately upon becoming pregnant. Anticoagulation is typically continued for at least 6 weeks postpartum, a window of especially high maternal clot risk.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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