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Antiphospholipid syndrome

Medically reviewed by Last updated on Feb 15, 2024.


Antiphospholipid (AN-te-fos-fo-LIP-id) syndrome is a condition in which the immune system mistakenly creates antibodies that attack tissues in the body. These antibodies can cause blood clots to form in arteries and veins.

Blood clots can form in the legs, lungs and other organs, such as the kidneys and spleen. The clots can lead to a heart attack, strokes and other conditions. During pregnancy, antiphospholipid syndrome also can result in miscarriage and stillbirth. Some people who have the syndrome have no signs or symptoms.

There's no cure for this uncommon condition, but medications can reduce the risk of blood clots and miscarriage.


Signs and symptoms of antiphospholipid syndrome can include:

Less common signs and symptoms include:

When to see a doctor

Contact your health care provider if you have unexplained bleeding from your nose or gums; an unusually heavy menstrual period; vomit that is bright red or looks like coffee grounds; black, tarry stool or bright red stool; or unexplained abdominal pain.

Seek emergency care if you have signs and symptoms of:


Antiphospholipid syndrome occurs when the immune system mistakenly produces antibodies that make blood much more likely to clot. Antibodies usually protect the body against invaders, such as viruses and bacteria.

Antiphospholipid syndrome can be caused by an underlying condition, such as an autoimmune disorder. You can also develop the syndrome without an underlying cause.

Risk factors

Antiphospholipid syndrome is more common in women than in men. Having another autoimmune condition, such as lupus, increases the risk of antiphospholipid syndrome.

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


Complications of antiphospholipid syndrome can include:

Rarely, in severe cases, antiphospholipid syndrome can lead to multiple organ damage in a short time.


If you've had episodes of blood clots or pregnancy loss that aren't explained by known health conditions, your health care provider can schedule blood tests to check for clotting and for the presence of the antibodies associated with antiphospholipid syndrome.

To confirm a diagnosis of antiphospholipid syndrome, the antibodies must appear in your blood at least twice, in tests conducted 12 or more weeks apart.

You can have antiphospholipid antibodies and never develop signs or symptoms. A diagnosis of antiphospholipid syndrome is made only when these antibodies cause health problems.


If you have blood clots, standard initial treatment involves a combination of blood-thinning medications. The most common are heparin and warfarin (Jantoven). Heparin is fast-acting and delivered via injections. Warfarin comes in pill form and takes several days to take effect. Aspirin is also a blood thinner.

When you're taking blood thinners, you have an increased risk of bleeding episodes. Your doctor will monitor your dosage with blood tests to be sure your blood is capable of clotting enough to stop the bleeding of a cut or the bleeding under the skin from a bruise.

There is some evidence that other drugs might be helpful in treating antiphospholipid syndrome. These include hydroxychloroquine (Plaquenil), rituximab (Rituxan) and statins. More study is needed.

Treatment during pregnancy

It's possible to have a successful pregnancy if you have antiphospholipid syndrome, especially with treatment. Treatment usually involves heparin or heparin with aspirin. Warfarin isn't given to pregnant women because it can affect the fetus.

Self care

Depending on your treatment plan for antiphospholipid syndrome, there are other steps you can take to protect your health. If you take blood-thinning medications, take extra care to keep from injuring yourself and to avoid bleeding.

Food and dietary supplements

Certain foods and medications may affect how well your blood thinners work. Ask your health care provider for guidance about:

Preparing for your appointment

In most cases, complications of antiphospholipid syndrome — such as DVT, stroke or pregnancy loss — will prompt you to seek medical care. Depending on your complication, you'll likely see a specialist in vascular disease, obstetrics or hematology.

Here's some information to help you get ready for your appointment.

What you can do

Be aware of any pre-appointment restrictions. When you make the appointment, ask if there's anything you need to do in advance. Make a list of:

Take a family member or friend along, if possible, to help you remember the information you get.

For antiphospholipid syndrome, some questions to ask your doctor include:

Don't hesitate to ask other questions, as well.

What to expect from your doctor

Questions your doctor is likely to ask include:

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