Antiphospholipid syndrome (APS), sometimes known as Hughes syndrome, is a disorder of the immune system that causes an increased risk of blood clots.

This means people with APS are at greater risk of developing conditions such as:

Pregnant women with APS also have an increased risk of having a miscarriage, although the exact reasons for this are uncertain.

APS doesn't always cause noticeable problems, but some people have general symptoms that can be similar to those of multiple sclerosis (a common condition affecting the central nervous system). Read more about the signs and symptoms of APS.

What causes antiphospholipid syndrome?

APS is an autoimmune condition. This means the immune system, which usually protects the body from infection and illness, attacks healthy tissue by mistake.

In APS, the immune system produces abnormal antibodies called antiphospholipid antibodies. These target proteins attached to fat molecules (phospholipids), which makes the blood more likely to clot.

It's not known what causes the immune system to produce abnormal antibodies. As with other autoimmune conditions, genetic, hormonal and environmental factors are thought to play a part.

Read more about the causes of APS.

Who's affected

APS can affect people of all ages, including children and babies.

However, most people with APS are aged between 20 and 50, and it affects three to five times as many women as men.

It's not clear how many people in the UK have the condition.

Diagnosing APS

Diagnosing APS can sometimes be tricky, as some of the symptoms are similar to multiple sclerosis.

Therefore, blood tests to identify the antibodies responsible for APS are essential in diagnosing the condition.

Read more about diagnosing APS.

How antiphospholipid syndrome is treated

Although there's no cure for APS, the risk of developing blood clots can be greatly reduced if it's correctly diagnosed.

An anticoagulant medicine such as warfarin or an antiplatelet such as low-dose aspirin is usually prescribed. These reduce the likelihood of unnecessary blood clots forming but still allow clots to form when you cut yourself.

Treatment with these medications can also improve a pregnant woman's chance of having a successful pregnancy. With treatment, it's estimated there's about an 80% chance of having a successful pregnancy.

Most people respond well to treatment and can lead normal, healthy lives. However, a small number of people with APS continue to experience blood clots despite extensive treatment.

Read more about treating APS.

Catastrophic antiphospholipid syndrome

In very rare cases, blood clots can suddenly form throughout the body, resulting in multiple organ failure. This is known as catastrophic antiphospholipid syndrome (CAPS).

CAPS requires immediate emergency treatment in hospital with high-dose anticoagulants.

Read more about catastrophic antiphospholipid syndrome (CAPS).

Page last reviewed: 09/11/2015

Next review due: 09/11/2017