Antiphospholipid syndrome

Antiphospholipid syndrome occurs when your immune system mistakenly attacks some of the normal proteins in your blood. Antiphospholipid syndrome can cause blood clots to form within your arteries or veins. It can also cause pregnancy complications, such as miscarriage and stillbirth.

Antiphospholipid syndrome may cause blood clots to form in your leg veins, a condition known as deep vein thrombosis (DVT). Antiphospholipid syndrome may also cause blood clots to form in organs such as your kidneys or lungs. Damage depends on the extent and location of the clot. For instance, a clot in your brain can cause stroke.

There's no cure for antiphospholipid syndrome, but medications can be effective in reducing your risk of blood clots.

Symptoms Causes Risk factors Complications

Signs and symptoms of antiphospholipid syndrome may include:

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

Other less common signs and symptoms include:

  • Neurological symptoms. Chronic headaches, including migraines, dementia and seizures are possible when a blood clot blocks blood flow to parts of your brain.
  • Rash. Some people develop a red rash with a lacy, net-like pattern (livedo reticularis).
  • Cardiovascular disease. Heart valves can be damaged in people with antiphospholipid syndrome.
  • Bleeding. Some people experience a decrease in platelets, blood cells necessary for normal clotting. If you have this condition (thrombocytopenia), you may have few or no symptoms. However, if your platelet count drops too low, you may have episodes of bleeding, particularly from your nose and gums. You can also bleed into your skin, which will appear as patches of small, red spots (petechiae).

Infrequent signs and symptoms include:

  • Movement disorder, in which your body and limbs jerk uncontrollably (chorea)
  • Cognitive problems, such as poor memory
  • Sudden hearing loss

When to see a doctor

If you already have an autoimmune condition, talk to your doctor about whether you should be tested for antiphospholipid antibodies.

Other reasons to contact your doctor include:

  • Pain or swelling in your leg or arm. See your doctor especially if an area of your leg or arm is red, swollen or tender. Seek emergency care if vein swelling and pain are severe or are accompanied by chest pain or shortness of breath, which could indicate DVT and an increased chance of a blood clot traveling to your lungs (pulmonary embolism).
  • Vaginal spotting or bleeding during pregnancy. This may be a sign of miscarriage or other pregnancy problems. However, many women spot or bleed and are able to have a healthy pregnancy. If you've had repeated pregnancy losses or unexplained severe complications of pregnancy, it could be related to antiphospholipid syndrome. Talk to your doctor about whether testing would be right for you.

If you have antiphospholipid syndrome and you're thinking of attempting pregnancy, treatments are available during your pregnancy. But be sure to seek the care of an expert obstetrical provider to discuss your options.

When it's an emergency

Seek emergency care if you have certain other serious signs and symptoms. Look for:

  • Signs and symptoms of stroke. These include sudden numbness, weakness or paralysis of your face, arm or leg; sudden difficulty speaking or understanding speech; sudden visual disturbances; sudden, severe headache; and dizziness.
  • Signs and symptoms of pulmonary embolism. These include sudden shortness of breath, chest pain and coughing up blood-streaked sputum.
  • Signs and symptoms of deep vein thrombosis. These include the development of leg swelling or pain.
  • Other signs of bleeding. These include unexplained bleeding from your nose or gums; an unusually heavy menstrual cycle; vomit that is bright red or looks like coffee grounds; black, tarry stool or bright red stool; and unexplained abdominal pain.

The role of phospholipids

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


There are two main classifications of antiphospholipid syndrome:

  • Primary. If there's no known underlying reason, such as an autoimmune disorder, you have primary antiphospholipid syndrome.
  • Secondary. If you have systemic lupus erythematosus or another autoimmune disorder, certain infections, or have taken certain medications, your antiphospholipid syndrome is secondary. The cause of your antiphospholipid syndrome is considered to be the underlying condition or medication.

Some factors are associated with developing antiphospholipid antibodies — though not necessarily with developing the syndrome. They include:

  • Infections. People with certain infections, including syphilis, HIV infection, hepatitis C and Lyme disease, among others, have a higher incidence of having antiphospholipid antibodies.
  • Medications. The high blood pressure medication hydralazine, the heart rhythm-regulating medication quinidine, the anti-seizure medication phenytoin (Dilantin) and the antibiotic amoxicillin may lead to an increased risk of developing antiphospholipid antibodies.
  • Genetic predispositions. Although the disorder isn't considered hereditary, research indicates that relatives of people with antiphospholipid syndrome are more likely to have the antibodies.

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.

Risk factors for developing symptoms

It's possible to have the antibodies associated with antiphospholipid syndrome without ever developing signs or symptoms. However, if you have these antibodies, your risk of developing blood clots increases particularly if you:

  • Become pregnant
  • Remain immobile for a period of time (such as when you're on bed rest or sitting during a long airline flight)
  • Have surgery
  • Smoke cigarettes
  • Take oral contraceptives
  • Have high cholesterol and triglycerides levels

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. This can result from decreased blood flow to your kidneys.
  • Stroke. Decreased blood flow to a part of your brain can cause a stroke, which can result in permanent neurological damage, such as partial paralysis and loss of speech (aphasia).
  • Cardiovascular problems. If a clot forms in your leg (deep vein thrombosis), the clot can damage the valves in the veins in your affected leg, which normally serve to keep the blood flowing upward to your heart. This may result in a condition called chronic venous insufficiency, which causes chronic swelling and discoloration in your lower legs, because of the impaired blood flow upward to your heart. Another possible complication is heart damage.
  • Lung problems. Complications related to your lungs may include high blood pressure in your lungs (pulmonary hypertension) and pulmonary embolism.
  • Pregnancy complications. These may include miscarriages, stillbirths, premature delivery and high blood pressure during pregnancy (preeclampsia).
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