The veins

In APS, blood clots (known medically as thrombosis) can occur in both the arteries and the veins. Clots in the arteries can cause strokes and heart attacks, while clots in the vein (known medically as venous thrombosis), can cause the vein to become swollen and painful due to the blood being unable to escape.

A blood clot can form in any vein of the body including the kidneys, liver, arms, fingers and thumbs, but the most common feature in APS is deep vein thrombosis (DVT).

DVTs usually occur in a deep leg vein not visible beneath the skin that runs through the muscles of the calf and thigh; most DVTs will form in the calf veins. People of all ages can be affected, with one person in every thousand in the UK developing a DVT each year. It is estimated that up to 10% of all these cases will test positive for antiphospholipid antibodies (aPL).

Some DVTs can happen without warning, while others are sometimes brought on by other factors such as immobility on long journeys, inactivity or dehydration, after surgery or a serious illness needing hospital admission. Patients admitted to hospital should be routinely screened for the risk of DVT and are often prescribed heparin injections. Women with APS should not take the oestrogen contraceptive pill or hormone replacement therapy (HRT) as these can increase the risk of DVT.

DVT usually (although not always) affects one leg and the symptoms can include pain, swelling and tenderness, particularly in the calf (the pain may be made worse by bending your foot upwards towards your knee); a heavy ache in the affected area; and the skin in the area of the clot may feel warmer and look red. Treatment with anticoagulation is almost always successful.

There are two main complications of DVT:

Pulmonary embolism

The main danger of a DVT is the risk of part of the clot breaking loose (known medically as an embolus), travelling through the bloodstream up the body and blocking one of the blood vessels in the lung causing a pulmonary embolism.

About one in ten people with an untreated DVT will develop a pulmonary embolism.

The pulmonary embolism blocks the blood supply to the lungs and is a potentially life-threatening condition. The symptoms will depend on the size of the blood clot and may include:

  • Shortness of breath
  • Rapid breathing
  • Light headedness
  • Feelings of anxiety and nervousness
  • Chest pain, which may be worse when you breathe in
  • Coughing up blood
  • Sudden collapse

It is very important to get treatment quickly as about 30% of people with untreated pulmonary embolism will die. The good news is that prompt diagnosis and treatment with anticoagulants can save lives and prevent further complications.

DVT and pulmonary embolism are collectively known as venous thromboembolism (VTE).

Post-thrombotic syndrome

If a DVT goes untreated, or a person has more than one DVT in the same leg, it is possible to develop long-term symptoms in the calf, known as post-thrombotic syndrome.

The symptoms occur because the blood clot in the vein of the calf can divert the flow of blood to other veins, causing an increase in pressure that can affect the tissues of the calf. This can result in calf pain, discomfort, swelling and rashes; in severe cases ulcers on the skin can develop. Post-thrombotic syndrome is also more likely to occur if the DVT forms in the thigh vein, or extends up into a thigh vein from a calf vein.