Factor V Leiden

6 min read

Thrombophilia is a broad medical term to describe the condition where your blood has an increased tendency to clot.

People with thrombophilia are more likely to develop a

deep vein thrombosis (DVT)
, a blood clot in one of the large veins in the leg.

It is important to be aware of the signs of a DVT and see your doctor as soon as possible if you think you may have one. DVT can cause pain, swelling and a heavy ache in your leg.

There are many different types of thrombophilia, many of which are inherited. The most common type of inherited thrombophilia is Factor V Leiden (the box on left of this page summarises the different types).

The blood clotting process

Normally, bleeding from an injury will trigger a chain reaction of different chemicals (clotting factors) in the blood. These chemicals cause a blood clot to form, which sticks to the injured part of the vessel along with blood particles called platelets.

Natural chemicals in the blood act against these chemicals to stop the blood clotting too much. In thrombophilia, this balance is upset and the person either has too much clotting factor, or too little of the substance that prevents clotting.

What are the symptoms of thrombophilia?

Often, thrombophilia is mild and many people do not experience any health problems.

You will only have symptoms if thrombophilia results in a blood clot.

Warning signs of a blood clot

People with thrombophilia are particularly at risk of developing a DVT. Warning signs of a DVT are pain, swelling and a heavy ache in a leg. Read more about the symptoms of DVT.

Sometimes, part of the blood clot can break away and travel through the blood circulation system and lodge in the lungs, causing a

pulmonary embolism (PE)
. A PE is a serious and potentially life-threatening condition, as it can prevent blood from reaching your lungs. Warning signs of a PE are chest pain or shortness of breath.
Read more about the symptoms of pulmonary embolism

See your doctor immediately if you have any of the above symptoms.

Who is affected by thrombophilia?

Some cases of thrombophilia are inherited – a tendency to form blood clots runs in the family and is passed on from parent to child.

However, not all cases of thrombophilia are linked with genes – some people acquire thrombophilia if they have a problem with their immune system, or as a result of another medical problem that has developed. People with acquired thrombophilia probably won't notice any problems until adulthood.

How is thrombophilia diagnosed?

Thrombophilia testing is not done routinely on everyone who develops a blood clot.

The disease may be suspected and tests may be done if you get an unexpected blood clot, given your health and age, or if a young member of your family (under the age of 40) had a blood clot.

It is diagnosed by blood tests that are carried out weeks or months after your blood clot. These tests look for deficiencies in your body's natural anticoagulants (anti-clotting chemicals). You usually have to wait until you have been off anticoagulant medicine (such as

) for four to six weeks.

If the results shows that you have thrombophilia, you may be referred to a haematologist, a specialist in diagnosing and treating blood disorders.

How is thrombophilia treated?

People with thrombophilia don't always need treatment, as it can be very mild and not cause any problems.

Treatment is necessary if you go on to develop a blood clot – you'll need treatment for the blood clot and treatment to prevent any further clots from developing. You may need to take [warfarin] injection, which are discussed below.

Warfarin and heparin

Warfarin and heparin are anticoagulants (anti-clotting medicine). They interfere with the clotting process and are commonly used to treat or prevent a DVT or PE.

Learn more about anticoagulants

If you just need an anticoagulant to prevent a clot, you will be prescribed warfarin (this takes a few days to work properly).

If you need instant treatment for an existing clot, you will usually be given a heparin injection (which works straight away) as well as warfarin tablets for the first few days. This injection will either be given in hospital, or at home (by a nurse or carer, or you can be taught to self-inject).

A heparin injection may also be given to people with

antiphospholipid syndrome
before and after surgery or during pregnancy. Unlike warfarin, heparin is safe to take in pregnancy.

International Normalised Ratio test

Your doctor will need to adjust your warfarin dose so your blood does not clot easily, but is not too high to put you at risk of bleeding problems. You will need to regularly have a blood test called the International Normalised Ratio (INR) to measure your blood clotting ability while on this medication.

The INR test will be done less frequently once your ideal dose has been reached – an INR of two to three is usually the aim.

Lifestyle advice

If you have thrombophilia, be aware of the symptoms of a blood clot (see above) and see your doctor immediately if you think you have one.

You should take the following precautions to lower your risk of blood clots:

  • lose weight if you are overweight
  • stop smoking if you are a smoker
  • follow a sensible diet and take regular exercise
  • try to avoid being immobile for prolonged periods, as this can cause a DVT (read more about
    preventing DVT

If you're pregnant, or planning to get pregnant, discuss this with your doctor and inform the midwife and obstetrician of your condition. You may need to take low-dose aspirin or an anticoagulant during your pregnancy, to help prevent pregnancy problems or a miscarriage.

If you're about to have a major operation, make sure you let the medical staff know about your condition, as you may need a heparin injection to prevent a blood clot forming.

Women with thrombophilia should avoid taking the combined oral contraceptive pill or

hormone replacement therapy (HRT)
, as these will increase your risk of a blood clot further.

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.