What Is Antiphospholipid Syndrome?

Medically Reviewed by Carmelita Swiner, MD on November 30, 2022
4 min read

It can be scary to find out that you have an autoimmune disorder with no cure. Antiphospholipid syndrome (APS) is one of those, but plenty of people with APS never have symptoms, and there are very good treatments for those who do.

APS is a disorder that affects how your blood clots, which can cause lots of issues in your body. It mostly affects young women, and sometimes the reason why you develop is unclear. But doctors do know a lot about how APS works and how to treat it.

About 1% to 5% of people in the United States have misbehaving antibodies (proteins) in their blood that can lead to APS. Normal antibodies fight infections, but with this condition, things called “autoantibodies” attack certain fats that help with blood clotting. And so your blood starts to clot abnormally.

APS antibodies can sometimes cause:

Plenty of people with the APS antibodies never have symptoms, though. For your doctor to diagnose APS, you must have both the antibodies and the symptoms.

No one is certain why some people develop APS antibodies, but doctors do know that your chances are higher if you:

Again, if you have the APS antibodies you might never show signs of APS. But you’re more likely to have symptoms of a blood clot if you:

Blood clots are the most common symptom of APS. Depending on where in your body a clot forms, it can cause different kinds of damage.

Deep vein thrombosis (DVT) is a blood clot that commonly occurs in the deep veins of the leg (the ones closest to the bones), which carry a lot of blood to the heart. A clot here can break off and cause all sorts of serious problems. DVT can also occur in other areas, such as the arms and pelvis. APS causes 15% to 20% of deep-vein thrombosis cases.

Brain clots in the blood vessels of the brain can also cause headaches, dementia, seizures, and strokes. Clots that travel to the lungs can cause a blockage in one of the pulmonary arteries (pulmonary embolism). And a clot in the heart can cause a blockage in the arteries there, heart valve damage, chest pain, and heart attack.

APS affects five times as many women as men. Because it primarily hits women in their 30s, it’s also linked to pregnancy complications. Women with APS can have a hard time getting pregnant, and blood clots that form in the placenta can cause miscarriage, premature birth, and development issues with babies.

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

If your doctor suspects APS, you have to take two blood tests. One or both of them has to be positive. And you have to be tested twice at least 12 weeks apart in order to confirm an APS diagnosis.

Blood thinners, which also are called anticoagulants, are one option against clots. Your doctor will first treat a clot with injected and then oral medication. To prevent another clot from happening again, some people have to take oral blood thinners for longer periods of time.

Pregnant women with APS get injections of blood thinners and low doses of aspirin for the entire pregnancy, up until just before delivery. Then they continue treatment after the baby is born.

It’s also important to treat any other conditions that put you at risk for blood clots, like high blood pressure, high cholesterol, obesity, diabetes, and other autoimmune disorders. You also need to stop smoking and stop estrogen therapy (either for menopause or birth control) if you have APS.