Patient Basics: Antiphospholipid Antibody Syndrome (APS)

Originally published by Harvard Health.

What Is It?

Antiphospholipid antibody syndrome (APS) is a condition defined by the presence of abnormal antibodies and a tendency to form blood clots or to have miscarriages.

People with antiphospholipid antibody syndrome produce antibodies that interact with certain proteins in the blood. This causes the blood to clot more than normal. The most commonly measured antiphospholipid antibodies include lupus anticoagulant and antibodies to cardiolipin or beta-2 glycoprotein.

The blood clots often form in the leg veins. The clots also can form in arteries. The blood clots may occur in any organ, but they tend to favor the lungs, brain, kidneys, heart and skin.

There are two types of APS: primary and secondary. People with primary APS do not have any associated condition. The secondary form is associated with another immune disorder, such as lupus, an infection or, rarely, the use of a medication (such as chlorpromazine or procainamide).

A person may have a blood test that detects antiphospholipid antibodies. This does not necessarily mean that he or she has APS or will develop symptoms or problems of APS.


The symptoms of APS can include any of the following:

  • Nervous system. APS can cause:
  • Stroke
    • Slurred speech
    • Difficulty understanding or forming words
    • Change in vision
    • Weakness on one side of the body
  • Involuntary jerking movements of the arms or legs
  • Dementia
  • Migraines
  • Other problems of the nervous system

In a form of APS called Sneddon’s syndrome, people have repeated strokes. They also have a mottling of the skin that is lacy purple and white.

Some people with APS develop a syndrome similar to multiple sclerosis. They can have:

  • Numbness
  • Double vision
  • Difficulty walking
  • Difficulty urinating
  • Heart valve problems that can mimic bacterial endocarditis
  • Blood clots in the upper chambers of the heart
  • Deep vein thrombosis (blood clot in a vein) that can pain and swelling in a leg or arm
  • Heart and blood vessels. APS can lead to:
    • Heart attacks (Up to 20% of younger people who have a heart attack have antiphospholipid antibodies.)

Antiphospholipid Antibody Syndrome

  • Blood cells. Some people with a condition called immune thrombocytopenic purpura (ITP) have antiphospholipid antibodies. The primary problem in ITP is low platelets, the blood cells that aid clot formation and prevent excessive bleeding. Over time, some people with ITP develop APS.       People with ITP and APS can have problems with excessive clotting and excessive bleeding.

Also, red blood cells can break down abnormally. This may cause fatigue, dizziness and pale skin. This is more common in people with lupus and secondary APS.

  • Lung. Blood clots in the lung can cause:
  • Chest pain
  • Shortness of breath
  • Rapid breathing

Repeated clots can cause elevated pressure in the blood vessels around the lungs. This may cause the person to be constantly short of breath.

  • Gastrointestinal. APS can affect the blood supply to the intestines, causing:
  • Abdominal pain
  • Fever
  • Blood in the stool

APS can cause a condition called Budd-Chiari syndrome. In this syndrome, a blood clot prevents blood from flowing out of the liver. The person may experience:

  • Nausea
  • Vomiting
  • Jaundice (yellow skin)
  • Dark urine
  • Pale stool
  • Swelling of the abdomen
  • Purple and white mottling of the skin
  • Repeated sores (ulcers)
  • Repeated bumps (nodules)
  • Tissue in the fingertips to die (gangrene)
  • Recurrent miscarriage which can occur early or late in pregnancy
  • A partial or complete separation of the placenta from the uterus before the baby is born
  • A small placenta
  • Premature birth
  • Kidneys. Blood clots that affect the kidneys can cause kidney damage and blood in the urine.
  • Skin. APS can cause:
  • Eyes. Veins or arteries in the retina can be affected. This can cause blurring or loss of vision.
  • Pregnancy. APS can cause problems for the fetus, such as:

It can cause problems for the pregnant woman such as stroke or blood clots in the lungs.

APS may be associated with a syndrome of pregnancy known as HELLP. HELLP stands for hemolysis (breakdown of red blood cells), elevated liver tests and low platelets.


Many symptoms that occur with APS are common even without the condition. They do not necessarily mean APS is the cause.

However, a doctor may order tests to detect the antibodies associated with APS when:

  • Blood clots or miscarriages occur for no apparent reason
  • A young person has a heart attack or stroke

People with antiphospholipid antibodies may have a positive screening test for syphilis even though they do not have the disease. Fortunately, confirmatory tests are available to rule out syphilis infection in a person with antiphospholipid antibodies.

Expected Duration

Some people with APS continue to have symptoms off and on throughout their lives. Others improve without any repeat episodes.

Some people even lose the antibodies associated with the syndrome. This can happen with primary APS. But it is especially common:

  • After a viral infection
  • In women who recently were pregnant
  • When a medication suspected to be associated with APS is no longer used


There is no known way to prevent APS. However, lifestyle changes can reduce the likelihood of blood clots.

To reduce your risk of blood clots:

  • Quit smoking
  • Increase physical activity
  • Avoid medications (if possible) that are suspected of increasing the risk of blood clots or causing APS


If you have antiphospholipid antibodies but have not had blood clots or a miscarriage, your doctor may recommend that you take a low-dose aspirin every day. However, aspirin increases the risks of bleeding. Your doctor will have to determine whether the uncertain benefits are worth the risks for you.

For people with a history of blood clots, doctors usually prescribe a powerful blood thinner called warfarin (Coumadin). This medication usually is taken for life. People who take warfarin need to have their blood tested regularly. That’s because if the blood is too thin, the risk of bleeding increases. If it is not thin enough, clotting is more likely.

Another commonly used blood thinner is called heparin. It may be used before you start taking warfarin. Heparin also is used for pregnant women, because warfarin is not safe for the developing fetus. Heparin is only available as an injection.

A woman with APS who is trying to become pregnant after repeated miscarriages may increase the chance of a successful pregnancy. She can do this by getting heparin injections and taking low-dose aspirin. This treatment should start as soon as the pregnancy is discovered. It continues until just before delivery.

Other medications used in advanced cases of APS include:

  • Steroids
  • Immune-suppressing drugs
  • Antiglobulin medications

However, the benefits of these medications have not been proven. And, they can cause significant side effects. They are used only for people who do not respond well to blood thinners.

When To Call a Professional

Contact a doctor if you have any symptoms of APS such as unexplained leg swelling or shortness of breath. Call your doctor if you have APS and want to become pregnant.


People with primary APS generally lead normal, healthy lives with the help of medication and lifestyle changes.

People with secondary APS generally have a similar prognosis. But their illnesses and life spans can be affected by associated conditions. APS associated with infections or medication use may be temporary and resolve once the infection subsides or a medication is stopped.

Some people with APS will have repeated blood clots despite the best treatments. This is referred to as catastrophic antiphospholipid antibody syndrome, a condition that, as the name suggests, can be fatal.

Additional Info

American College of Rheumatology
1800 Century Place
Suite 250
Atlanta, GA 30345-4300
Phone: 404-633-3777

National Institute of Arthritis and Musculoskeletal and Skin Diseases
Information Clearinghouse
National Institutes of Health
1 AMS Circle
Bethesda, MD 20892-3675
Phone: 301-495-4484
Toll-Free: 1-877-226-4267
TTY: 301-565-2966

National Organization for Rare Disorders (NORD)
55 Kenosia Ave.
P.O. Box 1968
Danbury, CT 06813-1968
Phone: 203-744-0100
Toll-Free: 1-800-999-6673
TTY: 203-797-9590