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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.

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.

© 2017 APS Support UK (trading name of the Hughes Syndrome Foundation). Registered Charity Number 1138116. A company limited by guarantee registered in England 7268671.