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Antiphospholipid syndrome (APS)

Find out about antiphospholipid syndrome, including symptoms, causes, treatment and when to get medical help.

About this information

This NHS content is written for people in England. Services, entitlements and contact routes may differ in other countries.

Symptoms of antiphospholipid syndrome (APS)

The main symptom of antiphospholipid syndrome (APS) is a blood clot, which can happen anywhere in the body.

Symptoms of a blood clot can include:

  • throbbing pain and swelling in 1 leg, usually the calf or thigh (rarely in both legs)
  • pain and swelling in your arm or tummy
  • warm, red or darkened skin around the painful or swollen area – this may be harder to see on brown or black skin
  • swollen veins that are hard or sore when you touch them
  • sudden breathing difficulties, chest pain and coughing up blood

These could be symptoms of deep vein thrombosis (DVT) or a pulmonary embolism.

Other symptoms of antiphospholipid syndrome can include:

  • joint pain
  • bleeding more easily than other people – signs include bruising easily and bleeding gums
  • a reddish-blue, lace-like rash on your lower legs – this may be harder to see on black or brown skin
  • having repeated miscarriages

Ask for an urgent GP appointment or get help from NHS 111 if you:

  • you think you have a blood clot

You can call 111 or get help from 111 online .

Call 999 or go to A&E now if:

  • you have severe difficulty breathing
  • you feel pain in your chest or upper back
  • your heart is beating very fast
  • someone has passed out

These could be signs of a pulmonary embolism or another serious condition which could be life-threatening and needs treatment straight away.

Find your nearest A&E

Causes of antiphospholipid syndrome (APS)

Antiphospholipid syndrome (APS) is an autoimmune condition, where your immune system attacks proteins in your blood, making your blood clot more easily.

Antiphospholipid syndrome is more common in women, and in people with another autoimmune condition, such as lupus.

How antiphospholipid syndrome (APS) is diagnosed

You may be offered a test to check for antiphospholipid syndrome (APS) if:

  • you had a blood clot and it's not obvious why you had it
  • you’ve had 3 or more miscarriages

You'll need to have 2 blood tests, 3 months apart, to confirm a diagnosis of antiphospholipid syndrome.

You may also need other tests, such as an ultrasound, CT scan or MRI scan, to check for blood clots.

Treatment for antiphospholipid syndrome (APS)

There's no cure for antiphospholipid syndrome (APS), but treatment can help prevent future blood clots.

You'll usually be given warfarin, a medicine to reduce your risk of blood clots (anticoagulant medicine).

Most people with antiphospholipid syndrome need to keep taking warfarin for the rest of their lives, as there's a high risk of having another blood clot in the future.

You may also need treatment for other conditions that increase your risk of a blood clot, such as high blood pressure or high cholesterol.

Important

If you have antiphospholipid syndrome, speak to your doctor before having any medical procedures or starting any new medicines (including contraception).

Some medicines may not be safe for you, and you may need extra treatment or monitoring during medical procedures.

Things you can do to reduce the risk of blood clots

If you have antiphospholipid syndrome (APS), there are things you can do to reduce the risk of a blood clot.

Do

  • get regular exercise

  • eat a balanced diet

  • try to keep to a healthy weight

  • drink plenty of water to avoid dehydration – you're more likely to get a clot if you're dehydrated

  • wear flight stockings or socks to improve your blood flow on long flights – a pharmacist can advise you about this

Don't

  • do not smoke

  • do not drink lots of alcohol – this can make you dehydrated

  • do not sit for long periods without moving, if you can avoid it

Complications of antiphospholipid syndrome (APS)

Antiphospholipid syndrome (APS) increases your risk of having a blood clot, which can cause many problems including:

Treatment to prevent blood clots (anticoagulant medicine) reduces the risk of these complications.

Antiphospholipid syndrome (APS)

Symptoms

Antiphospholipid syndrome (APS)

Causes

Antiphospholipid syndrome (APS)

Diagnosis

Antiphospholipid syndrome (APS)

Medical treatments

Antiphospholipid syndrome (APS)

Self-care

Antiphospholipid syndrome (APS)

Complications

The main symptom of antiphospholipid syndrome is a blood clot, such as deep vein thrombosis (DVT).

Antiphospholipid syndrome is caused by your immune system attacking proteins in your blood, making it clot more easily.

You may be offered a test for antiphospholipid syndrome if you've had a blood clot with no obvious cause, or multiple miscarriages.

Antiphospholipid syndrome is treated with anticoagulant medicines to reduce your risk of another blood clot.

Things you can do to reduce the risk of having another blood clot include getting regular exercise, eating a balanced diet, and stopping smoking.

Antiphospholipid syndrome increases your risk of blood clots, heart attack and stroke. But treatment reduces the risk of this happening.

Content supplied by the NHS website

Content supplied by the NHS website, refreshed 19 August 2026. View the original NHS article ↗

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