What to Know About Antiphospholipid Syndrome

Medically Reviewed by Zilpah Sheikh, MD on February 27, 2024
8 min read

Antiphospholipid syndrome (APS) is a rare immune system disorder that can cause clots to form in your blood vessels. This raises your risk for several types of health problems, including heart attack, stroke, and miscarriage.

Your immune system normally makes proteins called antibodies to protect you from unhealthy invaders like viruses. But when you have antiphospholipid syndrome, it makes antibodies that attack fat molecules throughout your body. That leads to cell damage, which makes your blood more likely to form clots in arteries and veins. The clots can form nearly anywhere in your body, from your brain to your lungs to your legs.

Scientists aren't sure exactly what causes APS, which is most common in young women (and those assigned female at birth). There's no cure, but treatment can help prevent blood clots from forming.

Antiphospholipid syndrome causes

About 1%-5% of people in the U.S. have such abnormal antibodies in their blood that can lead to antiphospholipid syndrome. But some people with these antibodies never show any signs of the disease. To be diagnosed with antiphospholipid syndrome, you must have both the antibodies and APS symptoms.

As with other autoimmune disorders, it's not clear what causes these antibodies to develop. Scientists think both genes and things in your environment are involved.

Antiphospholipid syndrome risk factors

Your chances of getting APS are higher if you:

  • Are female or were assigned female at birth (some 70% of those with APS are female)
  • Have a bacterial or viral infection, such as HIV, syphilis, hepatitis C, or Lyme disease
  • Take the antibiotic amoxicillin or certain blood pressure, heart-rhythm, and anti-seizure medications
  • Have lupus (up to about half of people with lupus also have APS) or another autoimmune disorder
  • Have relatives with APS

If you have APS antibodies, you're more likely to develop blood clot symptoms when you:

Antiphospholipid syndrome affects five times as many women as men and is most often diagnosed in women in their 30s. That's one reason it’s linked to pregnancy complications.

Another reason is that pregnancy increases your risk for blood clots even when you don't have APS antibodies. More blood flows through your body to help support the fetus. This puts extra pressure on your blood vessels, which can make them narrower. Pregnancy hormones also make clotting more likely.

Pregnancy complications linked to APS include:

  • A hard time getting pregnant
  • Preeclampsia (high blood pressure)
  • Miscarriage, usually after the 10th week of pregnancy
  • Premature birth, usually before the 34th week of pregnancy
  • Babies born small or underweight

Treatment for APS can reduce your risk for these complications.

How does antiphospholipid syndrome cause miscarriages?

Scientists think that blood clots in the placenta, the organ that provides nutrition and oxygen to the fetus during pregnancy, are to blame. The clots are thought to block the flow of nutrients through the placenta and into the umbilical cord, which keeps them from reaching the fetus.

Blood clots are the most common symptom of antiphospholipid syndrome. Their symptoms vary depending on where in your body the clot forms. They may include:

  • Pain in your chest
  • Nausea
  • Shortness of breath
  • Pain, redness, and swelling in your legs or arms
  • Changes in your speech pattern
  • Discomfort in your neck, back, arms, and jaws
  • Repeated miscarriages

Other symptoms might include:

  • Bleeding from your nose or gums resulting from low levels of platelets (cells that help your blood clot)
  • Anemia, which happens when you don't have enough red blood cells
  • A rash that makes a lacy red or purplish pattern on your skin
  • Damage to your heart valves
  • Frequent headaches
  • Memory problems

If you think you're having symptoms of a blood clot, get medical help immediately. Clots can be dangerous and even deadly.

Blood clots due to antiphospholipid syndrome can cause complications that may be serious, such as:




Antiphospholipid antibody test

If your doctor suspects you have APS, they'll give you blood tests to look for the three APS antibodies:

  • Anticardiolipin
  • Beta-2 glycoprotein I (β2GPI)
  • Lupus anticoagulant

You'll need to be tested two times, at least 12 weeks apart. At least one of the three blood tests must come back positive twice for you to be diagnosed with APS.

Antiphospholipid syndrome criteria

Just having the antibodies doesn’t mean that you have antiphospholipid syndrome. You also must have a history of health problems related to it. Most cases of APS are diagnosed after a clotting incident or a series of miscarriages.

There's no cure for antiphospholipid syndrome, but treatment can protect against complications. The goal of treatment is to stop new blood clots from forming and keep any you already have from growing larger.

A combination of blood thinning drugs (anticoagulants) is the standard treatment. Most people take fast-heparin as a shot along with a slower-acting blood thinner in pill form called warfarin (Jantoven). Low-dose aspirin is another blood thinner. You're at higher risk for bleeding when you take these drugs, so your doctor will keep an eye on that.

APS treatment during pregnancy

Treatment helps prevent miscarriages and other pregnancy complications of APS. During p regnancy, you can get injections of heparin up until just before delivery. You may also take low doses of aspirin. But warfarin isn't safe during pregnancy.

If you've had repeated miscarriages, your doctor may treat you with:

  • Enoxaparin, an anticoagulant you get in a shot
  • Corticosteroids, which suppress an overactive immune system
  • Immunoglobulin, another drug used to treat immune system disorders, which you get through an IV

If you have antiphospholipid syndrome, you'll probably need to take medication for the rest of your life.

Warfarin can interact with many other medications, so inform your doctor about all prescription or over-the-counter drugs you take. If you take low-dose aspirin to treat APS, be careful about taking over-the-counter painkillers or cough medications that might also contain aspirin.

Blood thinners can lead to excessive bleeding. So, call your doctor right away if you notice any of these signs:

  • Heavier-than-usual periods
  • Nosebleeds 
  • Bleeding from your gums
  • Blood in your poop or poop that looks black
  • Vomit that's red or looks like coffee grounds
  • Sudden vision problems
  • Serious head or abdominal (belly) pain
  • Trouble moving your arms or legs

It’s also important for people with APS to get treatment for other conditions that raise their risk for blood clots, such as:

Avoid estrogen therapy (such as for menopause symptoms or birth control), which also makes clotting more likely.

Lifestyle changes

If you're diagnosed with APS, stop smoking , which harms your blood vessels and raises your risk for clots. Ask your doctor if you need help quitting.

Keeping your weight in a healthy range reduces your risk for other conditions that make blood clotting more likely, such as heart disease. A balanced diet that's rich in fruits and vegetables can help with weight control.

But if you take heparin, don't suddenly add large amounts of foods rich in vitamin K to your diet without talking to your doctor first. These include leafy greens such as kale, spinach, and collard greens. Too much vitamin K could keep heparin from working as it should. These foods are healthy, so there's no need to avoid them completely. Tell your doctor if you want to increase your intake so they can monitor your blood.

If you take blood thinners, ask your doctor before taking supplements that may raise your risk of bleeding, such as:

  • Ginger
  • Ginkgo
  • Vitamin E

Avoid drinking more than two or three alcoholic drinks a day while taking warfarin. Alcohol can interfere with the drug's effectiveness. So can large amounts of cranberry juice; drink it in moderation.

Regular physical activity also helps reduce your risk of conditions such as diabetes and heart disease. If you take blood thinners, your doctor may recommend that you avoid contact sports that could lead to injury.

Antiphospholipid syndrome is an immune system disorder that makes your blood more likely to clot. This can lead to several health problems. While there's no cure, treatment can protect you against complications.

What is the main cause of antiphospholipid syndrome?

Sometimes a health condition, such as lupus or another autoimmune disorder, causes you to develop APS. That's called secondary antiphospholipid syndrome. But you can get APS even if you don't have another condition (primary phospholipid syndrome). Scientists think genetics is at least partly to blame.

What is the life expectancy of someone with antiphospholipid syndrome?

Most people with APS can expect to live normal, active lives, especially if they get prompt treatment. Less than 1% of people with APS go on to develop catastrophic antiphospholipid syndrome (CAPS), which causes blood clots throughout the body that damage multiple organs. About half of those with CAPS die from these complications.

Can antiphospholipid syndrome go away?

The condition affects different people in different ways. It's possible to have just one episode of APS symptoms and then get better. The abnormal antibodies that lead to APS can increase or decrease. A few people can even stop making these antibodies altogether.