Most blood clots are small and don't cause any symptoms. Your body will often be able to gradually break them down and there won't be any long-term effects to your health.
Larger clots can be more of a problem as they can partly or completely block the blood flow in your vein. This may cause symptoms in your affected leg or arm, for example:
- pain and tenderness
- warm skin that looks red
- a mild fever
Your GP will ask about your symptoms and examine you. If your GP thinks you might have deep vein thrombosis (DVT), he or she will refer you for some tests. You may have these on the same day you're referred.
The tests may include the following.
- A blood test called a D-dimer. This measures a substance that develops when a blood clot breaks down. If this test is negative it's unlikely that you have DVT, though it may be positive or raised for various other reasons.
- Ultrasound Doppler. This uses sound waves to look at your blood as it flows through your blood vessels. You may need to have more than one ultrasound.
- Venography. A special dye, which shows up on X-ray, is injected into your vein and X-rays of your leg are taken. This may be done if a D-dimer test or ultrasound doesn’t show anything abnormal but your doctor still suspects that you may have DVT.
Treatment for deep vein thrombosis (DVT) aims to reduce the risk of, and if possible, prevent complications such as pulmonary embolism. A pulmonary embolism happens when the blood clot (or a piece of it that has broken off) travels in your blood to your lungs (see Complications of deep vein thrombosis). Treatments also try to relieve any symptoms of DVT, such as pain and swelling.
You might need to go into hospital for some types of treatment, or if you're at risk of complications.
Try to start walking as soon as possible after DVT. This is perfectly safe and it may help your blood to circulate in your leg. It may also help to ease your symptoms and reduce your risk of developing complications.
Your doctor will give you anticlotting (anticoagulant) medicines to treat DVT. Anticlotting medicines help to stop blood clots getting bigger, or coming loose and travelling to your lungs. They can also stop new blood clots from forming. There are a number of anticlotting medicines, which include heparin injections, warfarin and newer oral tablets called rivaroxaban and apixaban. You’ll probably need to take anticlotting medicines for at least three months.
Some things can affect how well your medicines work. For example, alcohol can increase your chance of getting side-effects from taking warfarin. Always read the patient information leaflet that comes with your medicine. If you have any questions, ask your pharmacist or GP for advice.
Your doctor will monitor you while you take anticlotting medicines and will give you blood tests to measure how well they are working. The number of times you need to see your doctor for this will depend on what medicine you're taking. If you're taking warfarin for example, you will need blood tests every day or every other day when you first start taking it. Depending on how well it works for you, you will then need to have these less often and eventually only every 12 weeks.
These are also called graduated compression stockings. They may reduce the risk of a getting another DVT or developing post-thrombotic syndrome (see our Complications section for more information). A nurse or pharmacist will give you the right type and size. You may need to wear them for at least two years after you develop DVT. If you have DVT in one leg, you only need to wear a stocking on that leg (not on both).
Inferior vena cava filters
If you can’t take anticlotting medicines for some reason, your doctor may recommend you have a filter fitted in your inferior vena cava. Your vena cava is a large vein in your abdomen (tummy) and blood travels in it from your lower body back to your heart. A filter will prevent any blood clot that's been dislodged from travelling to your heart and then to your lungs where it could cause pulmonary embolism. Our Complications section has more information about this. You will have the filter removed as soon as you're able to take anticlotting medicines, or no longer need it.
Anyone can get deep vein thrombosis (DVT) but certain things can increase the risk. Often, more than one of these will contribute to you developing DVT. Some of the things that increase the risk of DVT include:
- your age – you're more likely to get DVT if you're over 60
- smoking (including passive smoking)
- having surgery
- immobility – for example, if you're bed bound or travelling long-distance
- having had DVT before
- having a condition that makes your blood clot more easily, such as thrombophilia
- having cancer
- taking a contraceptive pill that contains oestrogen, or taking hormone replacement therapy (HRT)
Long-haul travel (travelling for longer than four hours) can increase your risk of developing DVT. People often talk about the risk of DVT from flying but the risk is mainly the result of being inactive for long periods of time. This can happen during any form of long-distance travel, whether by car, bus, train or air. Therefore, you may hear the phrase ‘travel-related DVT’.
Generally, your risk of developing DVT when travelling is small unless you have one or more things that increase your risk (see the Causes section for more information). If you do have one or more of these, talk to your GP before you plan to travel.
Deep vein thrombosis (DVT) may not cause you any further problems. However, possible complications of DVT can include the following.
This is the most serious complication of DVT. A pulmonary embolism happens when the blood clot (or a piece of it that has broken off) travels in your blood to your lungs, where it blocks one of your blood vessels. This is serious and can even be fatal.
This can happen if DVT damages the valves in your veins and affects how they return blood from your lower leg to your heart. It can lead to high pressure in the veins in your legs and can eventually cause long-term pain and swelling. If the condition becomes severe, you may develop ulcers on your legs.
Ask your GP for advice if you think you're at risk of developing deep vein thrombosis (DVT).
There are things you can do to reduce your risk, such as stopping smoking if you smoke, or losing weight if you're overweight. Regular walking can help to improve the circulation in your legs and help to prevent a DVT from developing. If you have had a DVT, you can usually start walking once you get home from the hospital, unless your doctor has told you otherwise.
Another way to prevent DVT is to wear a geko device. This looks like a small wristwatch and you attach it below your knee. It stimulates the muscles in your leg and foot, which might reduce the risk of blood clots forming. It might be an option if you cannot move around much after surgery for example, or you can't take medicines. This device may be used if other treatment options haven’t worked or aren’t suitable for you. Ask your doctor for more information.
If you're having surgery
Surgery and some medical treatments can increase your risk of developing DVT. So if you're going to hospital for an operation, you will usually have an assessment to check your risk of developing DVT during surgery. There are many things that can be done to try to keep this risk as low as possible.
You may be given anticlotting medicines before and after surgery, or be asked to wear compression stockings. You may also be given a mechanical pump to use on your feet and legs after your operation. This is called an intermittent compression device. The pump automatically squeezes your feet and lower legs to help your blood circulate.
If you're travelling
If you have recently had treatment for DVT, you will need to wait two weeks before you take journeys over four hours long.
It's unlikely you will develop DVT when you travel. However, there are some steps you can take to reduce your risk of developing a blood clot on long journeys.
- Take short walks – if you're a passenger, walk up and down the aisle of the train or plane. Don’t take sleeping tablets – if you’re asleep throughout the journey, you won’t be able to move around and keep your legs active.
- Exercise the muscles of your lower legs as these act as a pump for the blood in your veins. Regularly bend and straighten your toes, ankles and legs.
- Wear loose-fitting clothes.
- Make sure you’re drinking enough fluids so you stay hydrated.
- Don’t drink too much alcohol as you may get dehydrated and feel less inclined to move around.
- Wear compression stockings if you have other risk factors for DVT (see Causes of deep vein thrombosis).
Are there any risks from taking warfarin to treat deep vein thrombosis?
Warfarin is an anticlotting medicine that you may need to take for several months after having deep vein thrombosis (DVT). Warfarin can have side-effects but you can reduce your risk of these by taking it as your doctor prescribes and having regular blood tests.
You take warfarin once a day and it's important that you take it at the same time every day. You can reduce your risk of side-effects by following the advice below.
- Make sure you go for your blood tests. You will have regular blood tests to monitor how well the medicine is working and to make sure you're taking the right amount. Too much can cause bleeding and too little can increase your risk of another clot forming.
- Carry an alert card or wear a medical bracelet that says you’re taking warfarin. It's important that anybody who treats you knows you're taking an anticlotting medicine because it can affect your treatment and interfere with other medicines.
- Don't drink cranberry juice or grapefruit juice if you're taking warfarin because either can affect the way that warfarin works in your body. Green vegetables that contain a lot of vitamin K can have an effect on warfarin too, as can alcohol. Talk to your doctor for more information before you make any changes to your diet.Many other medicines can interfere with warfarin, so tell your doctor when they prescribe any new medications that you’re on warfarin. If you become ill – contact your doctor for advice.
- If you have abnormal bleeding, such as bruises, bleeding gums, blood in your urine, black faeces or nose bleeds, seek urgent medical advice. It may be a sign that your dose of warfarin is too high.
- If you are, or think you may be pregnant, don't take warfarin as it can harm your baby. Get urgent advice from your GP about alternative anticlotting medicines.
I've had deep vein thrombosis – am I at risk of getting it again?
About a third of people who have deep vein thrombosis (DVT) or a pulmonary embolism will have another one within 10 years of the first. However, your chance of having DVT again depends on your personal circumstances. You’re more at risk if your first DVT wasn't caused by having surgery or an accident, for example.
Having a DVT increases your chance of having one again. You're more likely to develop a DVT again if the first one occurred without an obvious cause, or you got it because of an underlying medical condition that hasn't gone away since. You're less likely to have another one if you developed a DVT because of a one-off event, such as an operation.
If you develop DVT, your doctor will probably first treat you with injections of an anticlotting medicine called heparin, then prescribe warfarin that you take as tablets. How long you need to take this medicine for will depend on what caused your DVT and how likely you are to develop it again. You may only need to take warfarin for a few months, but it’s possible that you will need to continue taking it for life. You may be advised to wear compression stockings for at least two years.
Because you’ve already had DVT, you’re be more likely to develop it after long-distance travel than someone who has never had DVT. Therefore, it’s important to get medical advice before you make any travel plans that involve long journeys.
I'm having an operation. How can I reduce my risk of deep vein thrombosis?
There are a number of things that can help to prevent deep vein thrombosis (DVT). Your surgeon or nurse will give you information about these.
Your risk of developing DVT after an operation depends on a number of things. These include the type of surgery you’re having and if you're at risk of DVT from anything else, such as if you smoke. Being inactive can increase your risk of DVT too. After an operation, you might need to spend a lot of time in bed and won’t be able to move around a great deal.
Your surgeon or nurse will assess you when you go into hospital for your operation and will develop a plan to help prevent DVT. Ways to reduce your risk of DVT may include the following.
- If you're taking the contraceptive pill, your surgeon may ask you to stop taking it and use other methods of contraception for a month before your operation.
- You may be asked to wear compression stockings until you're back to your usual levels of mobility and activity after your operation. These can be attached to a device that fills the stockings with air and then deflates them, helping to squeeze your leg muscles.
- Get up and move around as soon as you can after your operation. You will also be shown some exercises to increase the blood flow in your legs and prevent clots.
- Make sure you drink enough fluids as soon as you're able to after your operation because this may help to prevent blood clots.
- You may need to have injections or take anticlotting medicine (anticoagulant tablets) to help thin your blood. Examples of these medicines include heparin, rivaroxaban and warfarin.
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