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Symptoms and Causes of DVT


Symptoms of DVT

The possible symptoms of Deep Vein Thrombosis can include:

  • Tender leg for no obvious reason – can be above knee, below knee or both
  • Swelling of ankle, ankle and calf, ankle, calf and thigh or even the whole leg
  • A heavy ache in the leg – especially on standing or walking
  • Warm skin in area of swelling
  • Sometimes the skin can be a bit redder but this is more common in phlebitis (inflammation of the vein wall)
  • DVT usually affects one leg, however it can affect both.

DVT usually affects one leg, however it can affect both.

Sometimes (estimated to be 50% of pateints) there are no symptoms and a DVT is only diagnosed if a complication occurs.


Causes of Deep Vein Thrombosis (DVT)

Blood is fluid when it flows through the arteries and veins. However it has to be able to clot in certain circumstances – for example to stop bleeding after a cut or graze.

In some circumstances the blood can clot when it still inside a blood vessel. When blood does this, either within an artery or vein, it is called a Thrombosis. The actual clot itself is called a thrombus – the condition of having a thrombus in a blood vessel is called thrombosis.

If a thrombus breaks away from the blood vessel wall and moves through the circulation with the blood, it is called an embolus. The condition caused by an embolus moving and getting stuck somewhere – often in the lungs – is called embolism.

A famous pathologist called Virchow pointed out in the 1920’s that there are 3 main causes for blood to clot when it is still in a blood vessel. These three factors are called – Virchow’s Triad.

  • Changes in the blood vessel wall
  • Changes in the blood flow
  • Changes in the blood composition

Changes in the blood vessel wall

Blood vessels are lined by a special sort of cell called an endothelial cell. This is a very flat sort of cell that has special properties, preventing normal blood clotting on it. Anything that damages the endothelial cell, can cause blood to clot on to it or to clot to the lining of the blood vessel underneath the endothelial cell.

Things that damage the endothelial cell include smoking or low oxygen concentrations.

The vessel wall can also change by having scars on it – such as having previous deep vein thrombosis – or bulges and narrowings of the vein walls as in varicose veins.

Changes in the blood flow

Humans, like all animals, really needs to be quite active. Unfortunately with modern day life, there are many instances where we are less active than we should be.

These might be for reasons we are unable to avoid, such as illness or breaking a leg, but also often due to our way of life such as sitting for long periods in front of a computer or television, travelling in cars, coaches or aeroplanes. By reducing the activity of the leg, the muscle pump is infused and so the blood flow becomes very sluggish in the deep veins.

Another cause for a change in the blood flow would be a change in the diameter or length of a vessel – such as found in varicose veins. Instead of the blood flowing smoothly up a narrow straight vessel, varicose veins with their bulges, narrowings, curves and kinks means the blood flow is altered and so clots are more likely to form.

Changes in the blood composition

The commonest cause of blood composition changes is dehydration. This often occurs because people drink alcohol or drinks with caffeine in them such as tea, coffee or some soft drinks. Unfortunately alcohol and caffeine act as diuretics, meaning that although fluid is being taken in, more is passed out in the form of urine. Therefore the blood becomes more concentrated and more likely to clot.

Females taking oestrogen either in the form of the oral contraceptive pill or as HRT, are also changing the blood composition in a way that makes thrombosis more likely. People with high blood fats (hyperlipidaemia) are also more likely to get clots due to an abnormal blood composition.

Deep vein thrombosis and cancer

Over the last few years, it has become increasingly well understood that deep vein thrombosis (DVT) can be the first sign of an underlying cancer, particularly in people over 40 years old.

The reason for this is not fully understood but it is likely that certain cancers, particularly of the bowel, breast, lung or pancreas secrete certain substances into the blood that increase the risk of DVT.

As such, anyone who is found to have a DVT for no good reason (a so-called ‘unprovoked’ DVT) should undergo full physical examination and tests to look for these common cancers.


‘Standard’ prevention, diagnosis and treatment of DVT

Most people who are doing things at high risk of Deep Vein Thrombosis DVT are given advice or help to reduce the risks:

  • When flying you are advised to wear properly fitted flight socks and to keep well hydrated
  • When having a general anaesthetic most patients have either TED stockings or heparin injections – or both
  • When in the heat, you are advised to drink water to keep well hydrated