Antiphospholipid syndrome (APS) is a disorder which is clinically manifested as recurrent venous or arterial thrombosis and/or fetal loss. It occurs when the immune system mistakenly attacks some of the normal proteins in the blood. Antiphospholipid syndrome can cause blood clots to form within the arteries or veins. It can also cause pregnancy complications, such as miscarriage and stillbirth.

Antiphospholipid syndrome may cause blood clots to form in the leg veins (deep vein thrombosis), but also in organs such as the kidneys or lungs, even a clot in the brain that can cause a stroke.


The symptoms of antiphospholipid syndrome may be:

  • Repeated miscarriages or stillbirths and other complications of pregnancy, such as premature delivery and high blood pressure during pregnancy (preeclampsia),
  • Blood clots in the legs (deep vein thrombosis, or DVT) that may travel to the lungs (pulmonary embolism),
  • Stroke,
  • Blood clots in the arteries of the arms or legs (peripheral arterial thrombosis).

But also neurological symptoms, rash, cardiovascular disease and bleeding.


In antiphospholipid syndrome, the body mistakenly produces antibodies against proteins that bind phospholipids, a type of fat present in the blood that plays a key role in coagulation. Antibodies are specialized proteins that normally attack body invaders, such as viruses and bacteria. When antibodies attack the phospholipid-binding proteins, the blood may clot abnormally.

Some factors like infections, medications and genetic predispositions are associated with developing antiphospholipid antibodies.

Risk factors

Risk factors for antiphospholipid syndrome include:

  • Having an autoimmune condition, such as systemic lupus erythematosus or Sjogren's syndrome,
  • Having certain infections, such as syphilis, HIV/AIDS, hepatitis C or Lyme disease,
  • Taking certain medications, such as hydralazine for high blood pressure, the heart rhythm-regulating medication quinidine, the anti-seizure medication phenytoin (Dilantin) and the antibiotic amoxicillin,
  • Having a family member with antiphospholipid syndrome.


Depending on which organ is affected by a blood clot and how severe the obstruction of blood flow to that organ is, untreated antiphospholipid syndrome can lead to permanent damage or death. Complications may include:

  • Kidney failure,
  • Stroke,
  • Cardiovascular problems,
  • Lung problems,
  • Pregnancy complications.


If you have antiphospholipid antibodies but do not take anticoagulant medication, take these precautions:

  • Inform the doctor that you have antiphospholipid antibodies.
  • Take measures to help prevent deep vein thrombosis if you can't move due to surgery or other medical reasons.
  • Don't smoke.
  • Take steps, such as lowering the cholesterol level, to help prevent a heart attack or stroke.