Venous thromboembolism (VTE), or the formation of blood clots in the veins, affects 10 million people worldwide every year.

A 2007 study in the United Kingdom of six European Union countries found that VTE-related deaths killed more people than Aids, breast cancer, prostate cancer and car crashes combined.

The condition is also on the rise in Singapore.

A 2009 study done by the Singapore General Hospital (SGH) found that the percentage of patients with deep vein thrombosis – a subset of VTE – increased threefold to 0.45 per cent (495 cases) of the total number of patients admitted to SGH, from 0.16 per cent (320 cases) in the years 1996-1997.

The increase could be due to the rising proportion of elderly patients here.

Yet, global public awareness of the condition and the steps that can be taken to prevent and treat it remains low, compared to other disorders involving blood clotting, such as heart attacks and strokes.

Here are four things you need to know about this potentially deadly condition:

1. WHAT IS VENOUS THROMBOEMBOLISM ?

Most people have a good idea of what is involved in a heart attack, but the term “venous thromboembolism” is likely to draw blank looks and some head-scratching.

The term is easier to understand if it is broken down into parts, said Associate Professor Lee Lai Heng, a senior consultant at SGH’s department of haematology.

A venous thrombosis is the blockage of a blood vessel by a blood clot, or thrombus.

A subset of VTE is deep vein thrombosis, where the blood clot that forms is found in a vein deep in the body, usually in the legs.

An embolism is what occurs when the thrombus dislodges from where it was formed and travels in the blood before becoming stuck in a narrower blood vessel elsewhere in the body.

Embolisms are dangerous and can be fatal if the clot ends up in the lungs, where it blocks some or all of the blood supply to this vital organ.

Blood clots in the lungs are known as pulmonary embolisms. Most pulmonary embolisms are caused by deep vein thrombosis.

Doctors have combined the two terms into one – venous thromboembolism – to refer to the overall medical condition.

2. WHAT ARE THE SYMPTOMS OF VTE?

VTE is a silent killer and the symptoms are non-specific, said Prof Lee.

Common symptoms of deep vein thrombosis of the lower limbs include pain, swelling and redness of the affected limb.

Patients affected by pulmonary embolisms can experience shortness of breath and giddiness.

When the condition is serious, there may be chest pain, fainting spells and coughing up of blood.

If it is left untreated, pulmonary embolisms can lead to sudden collapse and death.

3. WHAT ARE THE RISK FACTORS FOR VTE?

VTE is most often due to secondary causes that result in long-term immobilisation.

These can include not moving for many hours following major surgery, paralysis resulting from strokes or related conditions, and prolonged sitting during longdistance travel or video-gaming sessions.

Age is a risk factor as well. “The risk increases sharply after the age of 40 and peaks for people aged from 60 to 79 years,” said Prof Lee.

Older people tend to suffer from chronic illnesses that predispose them to VTE.

However, deep vein thrombosis or pulmonary embolisms can also occur in young people, especially if they have a family history of VTE.

4. HOW IS VTE TREATED AND WHAT ARE THE CHANCES OF RECOVERY?

Most people who are otherwise healthy should aim to prevent VTE from developing by avoiding prolonged immobilisation and dehydration, said Prof Lee.

Early diagnosis can often lead to recovery, so people with a family or past history of VTE should inform their doctors about it when seeking treatment for related symptoms.

For more serious cases which require hospitalisation, preventive measures such as blood-thinning medication or calfpumps are used.

Blood thinners, also known as anticoagulants, work by breaking up blood clots and preventing new ones from forming.

American presidential candidate Hillary Clinton takes blood-thinning medication daily after suffering deep vein thrombosis in 1998 and 2009, and a blood clot in her head in 2012 following a concussion.

Calf pumps improve blood circulation in the legs through compression, which squeezes blood in the veins back up the leg and thus prevents clotting.