In antiphospholipid syndrome (APS), the immune system produces abnormal antibodies that make the blood "stickier" than normal.

This means people with APS are more likely to develop blood clots in their veins and arteries, which can cause serious or life-threatening health problems.

These include:

• high blood pressure
• deep vein thrombosis (DVT)
• a stroke or a transient ischaemic attack (TIA) ("mini-stroke")
• heart attacks
• pulmonary embolism (a blockage in one of the blood vessels in the lungs)

People with APS may also experience any of the following symptoms:

• balance and mobility problems
• vision problems, such as double vision
• speech and memory problems
• a tingling sensation or pins and needles in your arms or legs
• fatigue (extreme tiredness)
• repeated headaches or migraines

Pregnancy problems

Women with APS have a much higher risk of developing complications during pregnancy, particularly if it's not treated.

Possible complications include:

• recurrent (3 or more) early miscarriages, usually during the first 10 weeks of pregnancy
• 1 or more later miscarriages, usually after week 10 of pregnancy
• premature birth, usually at or before week 34 of pregnancy, which may be caused by pre-eclampsia (where a woman develops high blood pressure during pregnancy)

Livedo reticularis

Livedo reticularis is a skin condition caused by small blood clots that develop inside the blood vessels of the skin.

It causes the skin to take on a blotchy red or blue appearance. Some people also develop ulcers (sores) and nodules (bumps).

These symptoms are often more severe in cold weather.

Superficial thrombophlebitis

Superficial thrombophlebitis is inflammation of the veins just under your skin, usually in your leg.

The symptoms are similar to DVT, but aren't usually as severe.

The symptoms of superficial thrombophlebitis include:

• swelling
• redness and tenderness along the affected vein
• a high temperature of 38C (100.4F) or above (although this is less common)

The symptoms usually resolve within 2 to 6 weeks.

Antiphospholipid syndrome (APS) is caused by the body's immune system producing abnormal antibodies called antiphospholipid antibodies.

This increases the risk of blood clots developing in the blood vessels, which can lead to serious health problems, such as:

• deep vein thrombosis (DVT)
• strokes
• heart attacks

It's not clear why these abnormal antibodies are produced, or why many people have antiphospholipid antibodies but don't develop blood clots.

A combination of genetic and environmental factors is thought to be responsible.

Antiphospholipid antibodies

Antibodies are proteins produced by the immune system to help fight off infection and illness.

They're part of the body's defence system and are produced to help protect against "foreign invaders", such as bacteria and viruses.

Antibodies signal the immune system to release chemicals to kill these bacteria and viruses, and to prevent infection spreading.

In APS, the immune system produces abnormal antibodies that rather than attacking bacteria and viruses, mistakenly attack proteins found on the outside of cells in the blood and blood vessels.

It's not known how this causes the blood to clot more easily.

But most experts believe that keeping your blood at the correct consistency (not too runny and not too sticky) is a delicate balancing act that relies on different types of proteins and fats working together.

This balance may be disrupted by the abnormal antibodies in people with APS.

Genetic factors

Research into the genetics around APS is still at an early stage, but it seems the genes you inherit from your parents may play a role in the development of abnormal antiphospholipid antibodies.

APS isn't passed down directly from parents to children in the same way as other conditions, such as haemophilia and sickle cell anaemia.

But having a family member with antiphospholipid antibodies increases the chance of your immune system also producing them.

Studies have shown that some people with APS have a faulty gene that plays a role in other autoimmune conditions, such as lupus.

This may explain why some people develop APS alongside another immune system condition.

Environmental factors

It's thought that one or more environmental triggers may be needed to trigger APS in some people.

Environmental factors that may be responsible include:

• viral infections, such as the cytomegalovirus (CMV) or parvovirus B19
• bacterial infections, such as E. coli (a bacteria often associated with food poisoning) or leptospirosis (an infection usually spread by certain animals)
• certain medications, such as anti-epileptic medicine or the oral contraceptive pill

Another theory is that many people with abnormal antiphospholipid antibodies only go on to develop APS if they have a higher risk of developing blood clots.

For example, if they:

• eat an unhealthy diet, leading to high cholesterol levels in the blood
• don't do enough exercise
• take the contraceptive pill or hormone replacement therapy (HRT)
• smoke
• are obese

But this doesn't explain why some children and adults who don't have any of these risk factors still develop APS.

An accurate diagnosis of antiphospholipid syndrome (APS) is important because blood clots can have serious consequences.

Diagnosis of APS is based on the results of specific blood tests and a medical assessment.

If APS is suspected, you'll usually be referred to hospital to see either:

• a haematologist (specialist in conditions affecting the blood)
• a rheumatologist (specialist in conditions affecting the immune system)

Specific blood tests

To diagnose APS, the blood needs to be tested for the abnormal antiphospholipid antibodies that increase the risk of blood clots.

This requires a blood test specifically designed to look for these antibodies.

A diagnosis of APS can only be made after 2 abnormal blood test results, with at least a 12-week gap between them.

This is because harmless antiphospholipid antibodies can sometimes develop in the body for short periods of time. 

Usually, this is the result of an infection or a side effect of medication, such as antibiotics.

If antiphospholipid antibodies are identified during the first blood test, another test will be needed at a later date to confirm whether the abnormal antibodies are still present.

Visit Lab Tests Online for more information about antiphospholipid antibody testing.

Medical assessment

If blood tests confirm you have APS, your medical history will be carefully assessed to check whether you have experienced any previous symptoms that may be caused by APS.

A diagnosis of APS can usually be confirmed if you have had:

• 1 or more confirmed blood clots
• 1 or more unexplained late miscarriages at or after week 10 of your pregnancy
• 1 or more premature births at or before week 34 of your pregnancy
• 3 or more unexplained early miscarriages before week 10 of your pregnancy

Treatment for antiphospholipid syndrome (APS) aims to reduce your risk of developing more blood clots.

Medication

As part of your treatment you'll be prescribed anticoagulant medicine such as warfarin, or an antiplatelet medication such as low-dose aspirin.

These work by interrupting the process of blood clot formation. This means blood clots are less likely to form when they're not needed.

Your treatment plan

Most people with APS need to take anticoagulant or antiplatelet medication daily for the rest of their life.

If blood tests show you have abnormal antiphospholipid antibodies, but you don't have a history of blood clots, low-dose aspirin tablets are usually recommended.

If you can't take aspirin, you may be prescribed an alternative antiplatelet tablet called clopidogrel.

Warfarin tablets are usually recommended if you have APS and a history of blood clots, such as previously having deep vein thrombosis (DVT) or a stroke.

But this needs to be changed if you become pregnant or are planning a pregnancy. Tell your doctor if this is the case.

If you develop a blood clot or your symptoms suddenly become severe, injections of an anticoagulant called heparin may be needed.

These injections may be given in hospital, or you may be trained to give them yourself.

Side effects

Side effects of these medications are uncommon and generally mild, such as indigestion or feeling sick (nausea).

But there's a risk that the disruption to the blood's ability to clot can cause excessive bleeding (a haemorrhage).

Symptoms of excessive bleeding can include:

• blood in your pee or poo
• black poo
• severe bruising
• prolonged nosebleeds (lasting longer than 10 minutes)
• blood in your vomit
• coughing up blood

Contact your GP immediately if you have any of these symptoms while taking an anticoagulant.

If this isn't possible, call your local out-of-hours service or NHS 111.

Treatment during pregnancy

Women diagnosed with APS are strongly advised to plan for any future pregnancy.

This is because treatment to improve the outcome of a pregnancy is most effective when it begins as soon as possible after an attempt to conceive.

Some medications used to treat APS can also harm an unborn baby.

If you don't plan your pregnancy, it may be several weeks before you realise you're pregnant.

This may increase the risk of treatment to safeguard the pregnancy being unsuccessful.

Treatment during pregnancy involves taking daily doses of aspirin or heparin, or a combination of both.

This depends on whether you have a history of blood clots and previous complications during pregnancy.

Warfarin isn't recommended during pregnancy because it carries a small risk of causing birth defects.

Treatment with aspirin or heparin, or both, is usually started at the beginning of the pregnancy and may continue for 1 to 6 weeks after you have given birth.

Lifestyle changes

If you're diagnosed with APS, it's important to take all possible steps to reduce your risk of developing blood clots.

Effective ways of achieving this include:

• not smoking
• eating a healthy, balanced diet – low in fat and sugar and containing plenty of fruit and vegetables
• taking regular exercise
• maintaining a healthy weight and losing weight if you're obese (have a body mass index of 30 or more)

Catastrophic antiphospholipid syndrome (CAPS) is a rare but serious complication of antiphospholipid syndrome (APS). It occurs in less than 1% of people with APS.

In people who develop CAPS, blood clots suddenly form throughout the body, resulting in multiple organ failure.

It's not clear what causes this, but 1 case in 5 occurs after an infection, trauma or surgery.

The initial symptoms can be wide-ranging, depending on which organs are involved.

Symptoms may include:

• loss of blood supply to the tips of your fingers or toes, causing them to go dark blue or black
• swollen ankles, feet or hands
• increasing breathlessness
• tummy (abdominal) pain
• blood in your urine 
• confusion
• fits (seizures)
• coma 

The symptoms usually develop suddenly and rapidly get worse.

Dial 999 and ask for an ambulance immediately if you or someone you know has APS that suddenly gets worse.

Immediate admission to an intensive care unit (ICU) is required for people with CAPS so the body's functions can be supported.

High-dose anticoagulants are used to stop the blood clots getting bigger while they're slowly absorbed by the body.

But even with the best available treatment, an estimated 50% of people die as a result of the condition.