An Overview of Antiphospholipid Syndrome

Woman With Leg Cramps

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Antiphospholipid syndrome (APS), also known as sticky blood, is an autoimmune disorder–the result of the immune system essentially turning on the body and attacking it in error. In the case of APS, the body makes antibodies to its own blood proteins, resulting in the formation of blood clots.

Antiphospholipid syndrome can occur in individuals without any associated disease. This is called primary APS. The disorder may also occur with systemic lupus erythematosus (SLE) or another autoimmune disorder. This is called secondary APS.

It is not yet known how frequently antiphospholipid syndrome occurs. APS antibodies can be found in as many as 50% of people with lupus and in about 1% to 5% of the rest of the population. APS most commonly occurs in young to middle-aged adults, but it can begin at any age.


Along with the antibodies, the body begins producing blood clots. The blood clots can block arteries and veins, cutting off blood supply to a part of the body. Symptoms depend on the location of the blood clots.

When clots occur in veins or arteries of the arms or legs, they may cause pain, swelling, numbness, tingling in the hands or feet, or leg ulcers. If the blood supply was completely cut off to a limb or extremity, such as a toe, amputation may be required.

Clots in the arteries of the heart may cause chest pain or heart attack, a heart murmur, or heart valve problems.

Clots in blood vessels of the skin may cause bruises (purpura) or a blotchy, purplish rash called livedo reticularis.

When clots occur in blood vessels of the brain, this can cause a stroke if the clot is blocking blood flow to the brain. A person with APS may also experience migraine headaches or seizures.

Pregnant women with APS may develop clots in the placenta during pregnancy, leading to a miscarriage or premature birth.

The most serious (and extremely rare) form of antiphospholipid syndrome, called catastrophic APS (CAPS), 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. In some cases, infection, trauma, or surgery appears to trigger the condition.


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.

Both males and females can have APS, though it is more common in females; having lupus or another autoimmune disease increases the risk of developing secondary APS.


Diagnosis of antiphospholipid syndrome relies on characteristic symptoms and signs, plus laboratory tests. If a person has had blood clots in the legs without any other possible cause, for example, APS may be to blame. If a woman is having recurring miscarriages or premature deliveries, APS may be suspected.

A blood test for anticardiolipin antibodies can help confirm the diagnosis. Other abnormal test results, such as decreased platelets or anemia, may be present. A computed tomography (CT) scan or magnetic resonance imaging (MRI) can confirm the presence of blood clots.


Treatment for antiphospholipid syndrome is based on a person's symptoms. For example, if someone has a stroke or heart attack as a result of APS, standard treatments for those are applied.

Catastrophic APS requires hospitalization. Those who are found to have the characteristic antibodies but no symptoms of APS may be started on daily low-dose aspirin to help reduce the risk of blood clots forming. If a blood clot is discovered, the person is started on anticoagulant medication such as Coumadin (warfarin) or Lovenox (enoxaparin).

A Word From Verywell

There is no cure for APS, but with medication and lifestyle modifications (such as avoiding long periods of inactivity in which clots can form in the legs), most people with primary antiphospholipid syndrome can lead normal, healthy lives. For those with secondary APS, adhering to your treatment plan for an autoimmune disease will keep you as healthy as possible.

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