Deep vein thrombosis (DVT) is a blood clot in a leg
vein. The common cause is immobility. A complication occurs in some
cases where part of the blood clot breaks off and travels to the
lung (pulmonary embolus).
This is done using ultrasound or a venogram
There is currently much research into the best method for
evaluating the most effective imaging modality based on the
evaluation of patient symptoms using the "Wells" scoring methodoly.
Link to Wells score evalualtion click here
venogram series of DVT in femoral vein
Leg Vein DVT
A deep vein thrombosis (DVT) is a blood clot that forms in a deep
leg vein. These are blood vessels which go through the muscles (they
are not the veins which you can see just below the skin). A calf
vein is the common site for a DVT. A thigh vein is less commonly
Why do blood clots form in leg veins?
Blood normally flows quickly through veins, and does not usually
clot. Sometimes a DVT occurs for no apparent reason. However, the
following increase the risk of having a DVT.
- Immobility which causes blood flow in the veins to be
slow. Slow flowing blood is more likely to clot than normal
- A surgical operation which lasts more than 30 minutes
is the most common cause of a DVT. The legs become still when
you are under anaesthetic. Blood flow in the leg veins can
become very slow.
- Any illness or injury that causes immobility
increases the risk of a DVT.
- Long journeys by plane, train, etc are thought to
cause a slightly increased risk of DVT. This is probably due to
sitting cramped for long periods.
- Faulty blood clotting is an uncommon cause. One example
is an inherited condition that causes the blood to clot more
easily than normal (factor V leiden).
- The contraceptive pill and hormone replacement
therapy (HRT) which contain oestrogen can cause the blood to
clot slightly more easily. Women taking 'the pill' or 'HRT' have a
small increased risk of DVT.
- Damage to the inside lining of the vein increases the
risk of a blood clot forming. For example, a DVT may damage the
lining of the vein. So, if you have already had a DVT, then you
have a higher than average risk of having another one sometime in
- Older people are more likely to have a DVT,
particularly if you have poor mobility or have a serious illness
such as cancer.
- Pregnancy increases the risk. About 1 in 1000 pregnant
women have a DVT.
- Obesity also increases the risk of having a DVT.
What are the symptoms of a deep vein thrombosis?
The typical symptoms are pain, tenderness, and swelling of the
calf. Blood that would normally go through the blocked vein is
diverted to outer veins. The calf may then become warm and red.
Sometimes there are no symptoms, and a DVT is only diagnosed if a
complication occurs (see below).
Sometimes it is difficult for a doctor to be sure of the
diagnosis as there are other causes of a painful and swollen calf.
For example, a muscle strain or infection. You will normally be seen
urgently at hospital if you have a suspected DVT. Tests may be done
to confirm the diagnosis.
Is a deep vein thrombosis serious?
When a blood clot forms in a leg vein it usually remains stuck to
the vein wall. The symptoms tend to settle gradually. But, there are
two main possible complications:
- Pulmonary embolus (a blood clot which travels to the lung).
- Post thrombotic syndrome (persistent calf symptoms).
In a small number of people who have a DVT, a part of the blood clot
'breaks off'. This travels in the bloodstream and is called an
embolus. An embolus will travel in the bloodstream until it becomes
stuck. An embolus that comes from a clot in a leg vein will be
carried up the larger leg veins to the heart, through the large
heart chambers, but will get stuck in a blood vessel going to a
lung. This is called a pulmonary embolus. A small pulmonary embolus
may not cause any symptoms. A medium sized pulmonary embolus can
cause breathing problems and chest pain. A large pulmonary embolus
can cause collapse and sudden death.
Without treatment, up to 6 in 10 people who have a DVT develop
long-term symptoms in the calf. This is called 'post-thrombotic
syndrome'. Symptoms occur because the increased flow and pressure of
the diverted blood in other veins can affect the tissues of the
calf. Symptoms can range from mild to severe and include: calf pain,
discomfort, swelling, and rashes. An ulcer on the skin of the calf
may develop in severe cases. Post-thrombotic syndrome is more likely
to occur if the DVT occurs in a thigh vein, or extends up into a
thigh vein from a calf vein.
The aims of treatment are:
- To prevent the clot spreading up the vein and getting larger.
This prevents the possibility of a large embolus breaking off and
travelling to the lungs.
- To reduce the risk of post-thrombotic syndrome developing.
- To prevent a further DVT in the future.
Anticoagulation - preventing the clot from getting bigger
Anticoagulation is often called 'thinning the blood'. However, it
does not actually thin the blood. It alters certain chemicals in the
blood to stop clots forming so easily. This prevents a DVT from
getting bigger, and prevents any new clots from forming. Warfarin is
the usual anticoagulant. However, it takes a few days for warfarin
tablets to work fully. So, heparin injections are often used in the
first few days for immediate effect. A serious embolus is rare if
you start anticoagulation treatment early after a DVT.
The aim is to get the dose of warfarin just right so the blood
will not clot easily, but not too much which may cause bleeding
problems. You will need regular blood tests whilst you take warfarin.
You need them quite often at first, but then less frequently once
the correct dose is found. (If you are pregnant, regular heparin
injections rather than warfarin tablets may be used.)
Compression and raising the leg - to prevent post-thrombotic
If the DVT was in a thigh vein, you may be advised to wear a medical
compression stockings. With this treatment the risk of developing
post-thrombotic syndrome is much reduced. You should wear the
stocking each day, for at least 2 years. (Symptoms of post-thrombotic
syndrome may develop even several months after a DVT, which is why
you should wear the stocking long-term.)
The slight pressure from the stocking helps to prevent fluid
seeping into the calf tissues from the outer veins which carry the
extra diverted blood following a DVT. The stocking also reduces, and
may prevent, calf swelling. This in turn reduces discomfort and the
risk of skin ulcers forming.
If you are advised to wear a compression stocking, you should put
it on each day whilst lying in bed before getting up. Wear it for
the whole day until you go to bed, or until you rest in the evening
with the leg raised. Take the stocking off before going to bed.
In addition, the following are also commonly advised.
- Raise your leg when you are resting. This too reduces the
pressure in the calf veins, and helps to prevent blood and fluid
from 'pooling' in the calves. 'Raised' means that your foot is
higher than your hip so gravity helps with blood flow returning
from the calf. The easiest way to raise your leg is to recline on
a sofa with your leg up on a cushion.
- Raise the foot of the bed a few inches if it is comfortable to
sleep like this. This is so your foot and calf are slightly higher
than your hip when you are asleep.
Preventing a first DVT - or a recurrence of a DVT
A DVT is often a 'one-off' event after a major operation. In this
situation you will normally be advised to stop taking warfarin after
a few months. Some people have an ongoing risk of a further DVT. For
example, if you have a blood clotting problem, or continued
immobility. You may then be advised to continue taking warfarin
Other things that may help to prevent a first or recurrent DVT
include the following.
- If possible, avoid long periods of immobility such as sitting
in a chair for many hours. If you are able, get up and walk around
now and then. A daily brisk walk for 30-60 minutes is even better
if you can do this. The aim is to stop the blood 'pooling', and to
get the circulation in the legs moving. Regular exercise of the
calf muscles also helps. You can do some calf exercises even when
you are sitting.
- Major surgical operations are known to be a risk for a DVT -
particularly operations to the hip, lower abdomen, and leg. You
may be given aspirin or heparin just before having an operation to
help prevent a DVT. An inflatable sleeve connected to a pump to
compress the legs during a long operation may also be used. It is
also common practice to get you up and walking as soon as possible
after an operation.
- When you travel on long plane journeys, train journeys, etc,
you should have little walks up and down the aisle every now and
then. Also, exercise your calf muscles every now and then whilst
sitting in your seat. A separate leaflet called 'Preventing DVT
When You Travel' gives more details.
- The main cause of DVT is immobility - especially during
- The most serious complication of DVT is a pulmonary embolus
where part of the blood clot breaks off and travels to the lung.
- Persistent calf symptoms may occur after a DVT.
- With treatment, the risk of the above two complications is
- Treatment includes anticoagulation, compression stockings, leg
elevation, and keeping active.
- Prevention is important if you have an increased risk of DVT.
For example, during long operations or when you travel on long