What is Antiphospholipid Syndrome?

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Antiphospholipid syndrome (APS), also known as "sticky blood," is an autoimmune disorder—the result of the immune system attacking the body in error. In the case of APS, the body produces antibodies that attack certain proteins that bind to phospholipids, a type of fat found in blood cells as well as in the lining of blood vessels. The result is the formation of blood clots, which can be serious and sometimes lead to a heart attack or stroke. APS occurs more frequently in women than in men and is a major cause of recurrent miscarriages and pregnancy complications. Blood thinners are the mainstay of treatment in APS.

Other names for antiphospholipid syndrome include:

  • Anticardiolipin antibody syndrome, or aCL syndrome
  • aPL syndrome
  • Hughes syndrome
  • Lupus anticoagulant syndrome

Types of Antiphospholipid Syndrome

There are three types of APS:

  • Primary APS, in which the disease occurs on its own, as opposed to in conjunction with another disorder.
  • Secondary APS, which occurs with another autoimmune disorder, most commonly systemic lupus erythematosus.
  • Catastrophic APS (CAPS), an extremely serious (and extremely rare) form of APS, occurs when many internal organs develop blood clots over a period of days to weeks, potentially causing life-threatening multi-organ failure. CAPS may develop in a person with primary or secondary APS, or in people without a previous diagnosis of APS. As many as half of those who develop CAPS do not survive.

Antiphospholipid syndrome is estimated to affect one in 2,000 Americans; 75% to 90% of those affected are women. 40% to 50% of people with lupus also have APS.


Symptoms of APS vary widely and depend on the location of the blood clots. Warning signs and symptoms that you might have a clot somewhere in your body include:

  • Pain, redness, warmth, and swelling in the limbs
  • A blotchy, purplish rash
  • Chest pain
  • Shortness of breath
  • Recurrent headaches, sometimes severe (or migraines)
  • Speech changes
  • Nausea
  • Shaking or involuntary muscle movements
  • Leg ulcers
  • Bleeding from the nose and gums
  • Heavy periods
  • Abdominal pain
  • Memory loss
  • Sudden vision changes
  • Confusion
  • Seizures
  • Vomit that's bright red or looks like coffee grounds
  • Tarry or bright red stools
  • Repeated miscarriages, premature births, or stillbirths

With APS, clots are twice as likely to form in the veins—the vessels that carry blood to the heart—as in the arteries, vessels that carry blood away from the heart.

APS may be discovered during a routine blood test, which will indicate a "prolonged thromboplastin time," a risk factor for blood clots. People with other autoimmune diseases, as well as women who are planning to undergo fertility treatments, are often screened for the antibodies as a precaution even if they haven't displayed symptoms.


Blood clots due to APS can cause serious and sometimes life-threatening complications, including the following.

  • Deep vein thrombosis (DVT): With DVT, blood clots form deep within a vein in the lower limbs or pelvis. DVT is a risk factor for, pulmonary embolism, a more serious complication.
  • Heart problems: APS can cause heart valve problems, including mitral valve regurgitation, in which the mitral valve does not shut properly, allowing blood to flow backward into the heart. APS also increases the risk of a heart attack.
  • Stroke: When a clot forms in a blood vessel that leads to the brain, the result can be a stroke. A milder version of a stroke, called a transient ischemic attack (TIA), is also a possibility. A TIA usually lasts only a few minutes and causes no permanent damage.
  • Pulmonary embolism: This can occur when a clot form travels through the bloodstream to the lungs (often as a result of DVT), causing chest pain and shortness of breath. A pulmonary embolism can block blood flow, raising blood pressure in the vessels leading to your lungs. This condition, called pulmonary hypertension, can lead to heart failure. 
  • Leg ulcers: When the lack of blood flow to the extremities is prolonged, the tissue in the affected areas can die; this is most common in the fingers and toes. If an ulcer progresses to gangrene, amputation may be necessary.
  • Thrombocytopenia: Thrombocytopenia, a condition characterized by low blood platelets, can cause easy or excessive bruising or bleeding.
  • Autoimmune hemolytic anemia: This autoimmune condition results in premature destruction of red blood cells by the immune system.

Pregnancy Issues

Women with APS are at increased risk for certain pregnancy complications due to the potential for a blood clot to form in the placenta. Risks include:

  • Late miscarriages (during the second or third trimester)
  • Recurrent miscarriages
  • Preeclampsia, a dangerous form of high blood pressure during pregnancy
  • Pre-term birth
  • Intrauterine growth restriction, a cause of smaller-than-average newborns
  • Development of deep vein thrombosis in mothers during pregnancy or post-partum

It is estimated that one out of five women with recurrent miscarriages have APL.

If you are diagnosed with APL and wish to become pregnant, it's important to find an obstetrician who specializes in high-risk pregnancies.


In APS, the body produces antibodies that target certain blood proteins that bind to phospholipids, a type of fat found in blood cells and in the lining of the blood vessels. The two most common proteins affected are called beta-2-glycoprotein I and prothrombin, but it is not understood exactly how this process leads to the development of blood clots.

There is no known cause of primary APS, though researchers believe that genetic and environmental factors play a role. In rare cases, APS has been found to run in families, suggesting a genetic predisposition. Some researchers have also linked certain viruses with APS, but more studies need to be done to confirm this connection.

Infection, trauma, or surgery sometimes appear to trigger CAPS.

Risk Factors

You are at higher risk for blood clots in general if you have diabetes, high blood pressure, high cholesterol, obesity, are a smoker, or take birth control medications or hormone replacement therapy that contains estrogen.

Risk factors for APL itself include being female or having another autoimmune condition. Some medications have been linked to APS, including hydralazine for high blood pressure, quinidine (for arrhythmias), the anti-seizure medication phenytoin (Dilantin), and amoxicillin, an antibiotic.

  • One out of five women with recurrent miscarriages have APS.
  • A third of strokes occurring in people under the age of 50 are due to APS.


Testing for APS is indicated for people who have had repeated unexplained blood clots and associated symptoms or complications, recurrent late-term miscarriages, or other pregnancy complications, such as premature births or fetal death.

Blood tests will look for three different antibodies, including:

  • Lupus anticoagulant
  • Anticardiolipin antibody
  • Anti-β2GP1antibody

When a test is positive for one of these antibodies on two or more occasions at least 12 weeks apart, the diagnosis of APS is confirmed.

Differential Diagnoses

Symptoms of APS can resemble those of other diseases. The following conditions may need to be ruled out in order to arrive at an accurate diagnosis.

  • Systemic lupus erythmatosus (or lupus): Lupus is an inflammatory autoimmune disorder that can affect various organ systems. It is the most likely disease to occur in people with secondary APS.
  • Multiple sclerosis (MS): MS is a chronic autoimmune disease affecting the brain and spinal cord. MS and APS share some of the same neurological symptoms.
  • Thrombophilias: This is the name for a group of rare genetic disorders that produce blood clots. They include protein C deficiency, protein S deficiency, antithrombin III deficiency, and factor V Leiden.


There is no cure for APS. The goal is to prevent blood clots from forming or recurring.

If you are found to have APS antibodies but no symptoms, your healthcare provider may prescribe daily low-dose aspirin to reduce the risk of blood clots forming. If a blood clot is discovered, anticoagulant medications (also called blood thinners) such as Coumadin (warfarin), Lovenox (enoxaparin), or heparin can help prevent future clots. Sometimes these medications are used in combination. Some can also be used safely in pregnant women with APS.

Because warfarin can cause excessive bleeding, if you take this medication you will require regular blood tests to make sure your blood is clotting sufficiently, and so dosages of the medication can be modified if necessary. These blood tests are known as international normalized ratio (INR) tests.

When blood clots result in serious complications, such as heart attack, stroke, or pulmonary embolism, you will receive standard treatment for those. Catastrophic APS requires immediate hospitalization; in this case, treatment may include anticoagulants, glucocorticoids, plasma exchange, and/or intravenous immunoglobulins.


Living with APS almost always requires taking blood-thinning medications indefinitely to prevent clots. To minimize the risk of excessive bleeding from these drugs, you will need to take certain precautions, such as:

  • Avoiding contact sports or activities that increase the risk of falling
  • Being extra careful when shaving and using knives, scissors, or other sharp tools
  • Talking to your healthcare provider to determine if it's safe for you to drink alcohol or cranberry juice, which may increase the blood-thinning effect of warfarin. Certain foods that are high in vitamin K (including broccoli, avocado, and chickpeas) may also interact dangerously with warfarin, as may certain over-the-counter medications and supplements: check with your practitioner about any dietary changes they may recommend.

To reduce your risk of blood clots in general, you should not smoke if you have APS, and you will need to work with your healthcare provider to effectively manage conditions such as high blood pressure, diabetes, high cholesterol, and obesity. Avoiding long periods of inactivity will also help prevent clots from forming in the legs. Taking hormone replacement therapy or birth control medications containing estrogen may also be contraindicated.

A Word From Verywell

There is no cure for APS, but with careful monitoring of blood-thinning medications as well as lifestyle modifications, most people with primary APS can lead normal, healthy lives. For those with secondary APS, adhering to your treatment plan for the co-occurring autoimmune disease will help keep you as healthy as possible.

10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. American College of Rheumatology. Antiphospholipid Syndrome.

  3. APS Foundation of America. Catastrophic Antiphospholipid Syndrome (CAPS).

  4. APS Foundation of America. Antiphospholipid Syndrome.

  5. National Organization for Rare Disorders. Antiphospholipid Syndrome.

  6. Andreoli L. SP0164 How to manage asymptomatic carriers of antiphospholipid antibodies. Annals of the Rheumatic Diseases 2018;77:43. doi:10.1136/annrheumdis-2018-eular.7811 

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  8. American Academy of Clinical Chemistry. Lab Tests Online. Antiphospholipid Antibodies.

  9. North American Thrombosis Forum. A Guide to INR Levels.

  10. Rodriguez-Pintó,I, Santacreu, I, Cervera, R, et. al. What is the best strategy in treating catastrophic antiphospholipid syndrome? Int. J. Clin. Rheumatol. (2015) 10(4), 245–255. doi:10.2217/ijr.15.25

Additional Reading

By Mary Kugler, RN
Mary Kugler, RN, is a pediatric nurse whose specialty is caring for children with long-term or severe medical problems.