Antiphospholipid syndrome (APS)

What is antiphospholipid syndrome (APS)?

Antiphospholipid syndrome (APS) is sometimes known as ‘sticky blood syndrome’ or Hughes syndrome. APS can cause blood clotting in your arteries or veins and is a major cause of recurrent miscarriage. It’s also one of the most common causes of strokes in young people. It’s estimated that 1 in 5 people who’ve had a stroke before the age of 40 may have APS.

APS affects all age groups but is most common between the ages of 20 and 50. It was first diagnosed in people who had lupus (systemic lupus erythematosus) but it was later discovered that APS can occur on its own (this is called primary APS).


The two main problems caused by antiphospholipid syndrome (APS) are blood clotting (thrombosis) and pregnancy problems, particularly recurrent miscarriage.

Blood clotting can occur in:

  • the veins, causing pain and swelling, typically in your calf (deep vein thrombosis or DVT) – this can sometimes lead to pulmonary embolism if a piece of the clot breaks away and travels to your lung
  • the arteries, causing high blood-pressure or strokes
  • the brain, which can cause memory loss, migraines, forgetfulness, slurred speech, fits or sight problems.

In pregnancy, APS can cause recurrent miscarriage. This can happen at any time during your pregnancy but is most common between 3 and 6 months. APS can also cause other pregnancy problems, such as high blood pressure (pre-eclampsia), small babies and early deliveries. APS is now recognised as one of the most important treatable causes of recurrent miscarriages.

Other problems sometimes associated with APS include:

  • Heart problems – The heart valves may thicken and fail to work, or your arteries may narrow because their walls get thicker, leading to angina.
  • Kidney problems – APS can cause narrowing of the blood vessels, resulting in high blood pressure.
  • Infertility – Testing for antiphospholipid antibodies (aPL) is becoming routine in infertility clinics.
  • Skin problems – Some people develop a blotchy rash, often seen on the knees or arms and wrists, with a lacy pattern (known as livedo reticularis).
  • Low platelet count – Some people with APS have very low platelet levels – often there are no symptoms, although people with very low counts may bruise easily or experience strange or excessive bleeding.

Very rarely, APS can cause clots to develop in small blood vessels in several parts of your body at once, causing damage to several organs at the same time and making you seriously ill. This is called catastrophic APS and is very rare. It’s thought to be triggered by things like infection, trauma, medication or surgery. You should have quick and easy access to your rheumatology or haematology team in these circumstances.


Antiphospholipid syndrome (APS) is an autoimmune disease, which means that it’s caused by your immune system attacking healthy parts of the body instead of fighting infections.

If you have APS, your immune system produces harmful antibodies called antiphospholipid antibodies (aPL) which attack proteins are linked to fats in your body. The most important of these proteins is called beta-2-glycoprotein I. When aPL stick to this protein they can interfere with blood cells. The cells change in such a way that the blood becomes sticky and more likely to clot inside the vessels. In a pregnant woman aPL can also affect the cells of the womb and the placenta, which can make the baby grow more slowly and increase the risk of miscarriage.

Although people with APS have a higher risk of thrombosis than other people, they may go for many years without suffering clots. Occasionally, the thrombosis occurs during an infection such as a sore throat; however, in the vast majority of people the thrombosis comes ‘out of the blue’. The risk of blood clots can be reduced by blood-thinning drugs and by reducing other factors that can cause clots, including:

  • smoking
  • immobility (related, for instance, to the thrombosis seen after long-haul flights)
  • the contraceptive pill
  • genetic factors – there may be a family history of clots, miscarriages, other autoimmune diseases such as lupus or thyroid problems.

How will antiphospholipid sydrome affect me?

Many people with APS feel very well and have no symptoms. The aim of treatment is to prevent thrombosis or miscarriage. This is achieved by an early diagnosis and the right combination of drugs. Other people with APS have symptoms like rash, joint pain, migraine and tiredness even when they don’t suffer thrombosis and are not pregnant. This is especially true in people who have lupus as well as APS.

Because the drugs are used to prevent symptoms, it means you may be taking drugs for many years even though you have no symptoms. As with all drugs there can be side-effects, so it’s important to balance the risk of side-effects against the risks of condition itself. With the right approach the outlook for most people with APS is good.


Antiphospholipid syndrome (APS) can only be diagnosed if:

  • you have a positive blood test and
  • you've suffered either thrombosis or miscarriage.

More and more people who have thrombosis or a miscarriage are routinely tested for APS. If you’ve had either of these problems, especially if they’ve happened more than once, you should discuss with your doctor whether you need these blood tests. Depending on the results, your doctor may want to refer you to a specialist (either a rheumatologist or haematologist).


There are three main blood tests used to diagnose APS. These are:

  • the anticardiolipin test
  • the lupus anticoagulant test
  • the anti-beta-2-glycoprotein I test.

All three tests detect whether aPL are present in the blood. The result of the lupus anticoagulant test is either positive or negative, while the results of the other two tests are given as numbers. The higher this number is, the more aPL a person has in their blood. Because these tests measure aPL in different ways, around 20% of people with APS will have a negative result in one test or the other. One test alone could therefore miss the diagnosis.

The tests are usually repeated after 12 weeks as levels of aPL vary and can sometimes go up when you have an infection. If you only have one positive test and it quickly becomes negative again then you probably don’t have APS.

Higher levels of antibodies (i.e. higher numbers in the anticardiolipin or anti-beta-2-glycoprotein I tests) suggest you may be at greater risk of blood clots and other symptoms. Being positive in more than one of the three tests also suggests a higher risk.

I repeatedly test positive for aPL. Does this mean I'll definitely get APS?

No, it doesn't mean that you’ll definitely develop APS. Many people who have lupus are tested for these antibodies and about 20–30% will be positive for aPL. People who carry the antibodies but who’ve never had either clots or miscarriages aren't said to have APS but to be aPL-positive.

Doctors have to decide whether people who are aPL-positive are at high or low risk of getting APS in the future. There’s no foolproof way of deciding, but factors that may help include:

  • how high the aPL level is
  • how many of the three tests are positive
  • whether there are other risk factors for thrombosis
  • whether you have other typical symptoms (such as migraine).

Am I being tested for lupus?

No, this confusion often arises because one of the blood tests for APS is called the “lupus anticoagulant” test. This is because it was first invented by doctors who were studying patients with lupus. In fact it is a test for APS, NOT a test for lupus. There are other, better blood tests for lupus itself and many people who are positive in the “lupus anticoagulant” test do not have lupus.


Antiphospholipid syndrome (APS) can’t be cured but the effects can be controlled. Treatment with anticoagulant (blood-thinning) drugs can help prevent both blood clots and miscarriages. The most commonly used drugs are aspirin, warfarin and heparin.

If you have aPL but no history of clotting, your doctor will probably recommend low daily dose aspirin (75–100 mg). This isn’t guaranteed to prevent blood clots but is known to make the blood less sticky. If you have other factors which increase your risk of clots, or if you suffer from typical APS symptoms such as migraine or livedo reticularis, your specialist may advise you to take warfarin instead of aspirin.

If you have APS and a history of clotting, you’re likely to be given warfarin to prevent further blood clots. Warfarin is taken by mouth. You’ll have regular blood tests (called an INR, or International Normalised Ratio) to check what effect the drug is having, and if necessary your dose will be adjusted. The INR blood tests can be just a finger-prick test or a sample of blood may be sent off for assessment by a laboratory. The most serious side-effect of warfarin during treatment is bleeding. This means that your dosage will be closely monitored.

Warfarin can interact with a number of drugs and foods (for example grapefruit juice), so it’s important that you’re aware of this and take steps to ensure your other medications or diet won’t affect the results of the blood tests.

If you’ve had a number of miscarriages, but no history of clotting, there are two considerations:

  • treatment during pregnancy to prevent another miscarriage
  • treatment outside pregnancy to prevent clots.

During pregnancy the usual treatment is low-dose aspirin; however, it’s common for pregnant women with APS to be given daily injections of heparin as well as aspirin, especially if the previous miscarriages happened in mid- to late pregnancy or if there have been other pregnancy complications such as pre-eclampsia.

It’s a good idea to be seen in a special pregnancy clinic where the doctors have experience of APS, as well as by your normal obstetrician. Most APS specialists have access to those clinics and you should ask about this if you’re planning to have a baby.

If you’re on warfarin and you become pregnant you’ll probably be changed over to heparin. This is because warfarin is potentially harmful to the baby.

Managing your symptoms

Learn how you can manage the symptoms of antiphospholipid syndrome.


Although there aren’t any specific exercises that can help with the condition, taking regular exercise will help keep you fit and keep your heart healthy.

Read more about exercise and arthritis.

Diet and nutrition

It’s been suggested that increasing the amount of essential fatty acids in your diet, particularly omega-3 fatty acids found in oily fish, could help reduce your risk of blood clots. However, there are no clinical trials to support this idea. As well as this, fish oils contain large amounts of vitamin A which can be harmful in pregnancy, so we wouldn’t recommend this if you’re thinking of having a baby. Eating a healthy, balanced diet is important for your general health and may help prevent you from developing blood clots. You should also keep to a healthy weight and stop smoking.

At present, no complementary therapies have been shown to help with APS.

Read more about diet and arthritis.

Reducing your own risk of getting clots

There are several things that you can do to help reduce your risk of getting clots:

  • Don’t smoke – smoking will increase your risk of clots.
  • Don't drink excessive amounts of alcohol.
  • Think very carefully about what sort of contraception to use and discuss it with your doctor, as some types of contraceptive pill increase the risk of clotting.
  • If you’re thinking about hormone replacement therapy after the menopause, this may also increase your risk of clots so you should discuss it with your doctor.
  • Think ahead if you know you’ll soon have to keep still in one place for a long time (for example on a long-haul flight) and see if you can take measures to avoid this (e.g. booking a seat with legroom or buying flight socks).
  • If you have another condition that can increase your risk of blood clots (e.g. diabetes, high blood pressure or high cholesterol) you should make sure you have regular checks to keep these factors under control.

Helping yourself with APS

It’s important that you understand the features of APS and therefore when to ask for help. You should have access to your local specialist team, which may include a specialist nurse who you can call for advice.

If you’re taking drugs such as warfarin you should be careful about accidents, as bruising can be worse. If you’re pregnant it’s important that you attend your clinic appointments and keep in touch with your specialist obstetric consultant, whose aim is always to keep you and your baby healthy.