Deep vein thrombosis (often abbreviated to DVT) is a common medical condition where a blood clot forms in a deep vein. It usually occurs in the leg. Here in the UK, deep vein thrombosis affects around 1 in every 1000 people each year.
This is a simple guide to the causes, symptoms, and treatment for DVT. It will also include helpful tips for preventing deep vein thrombosis.
What is Deep Vein Thrombosis?
Deep vein thrombosis (or DVT) is a blood clot in a vein. In most cases, it affects the deep veins in the legs. Deep leg veins are large blood vessels that run through the muscles of your calf and thigh. Blood clots that develop in other veins are called venous thrombosis.
DVT can develop at any time. However, it is most common in people over the age of 40, overweight people, and those who smoke. Deep vein thrombosis can also lead to dangerous complications, including pulmonary embolism. Thrombosis UK gives the following definition:
Pulmonary embolism (PE) occurs when a piece of a blood clot breaks loose into the blood stream and travels to the lungs, causing a blockage in a blood vessel in the lungs.
Pulmonary embolism can be life-threatening, so it's important to seek treatment straight away if you notice any of the symptoms of deep vein thrombosis or PE. When these two conditions (DVT and PE) occur together, it is known as venous thromboembolism.
Causes of Deep Vein Thrombosis
There are a number of different factors that can increase your risk of deep vein thrombosis. These include:
- Blood vessel damage.
- Inactivity for long periods - after surgery or during a long journey, for example.
- A family history of blood clots.
- Certain medical conditions such as cancer, heart disease, rheumatoid arthritis, and thrombophilia.
- Hormone replacement therapy.
- Contraceptive pills (especially those containing oestrogen)
What Causes Blood Clots?
Blood clots form when the blood thickens. This happens naturally after an injury to prevent bleeding, so it's normally a very useful process. Platelets in the blood stick together and form a scab to plug up the injury, preventing blood loss. However, when this process occurs without an obvious cause, like in DVT cases, blood clots can be a serious health risk. They can prevent the blood from flowing properly and reaching the heart, lungs, or brain.
Next, we'll take a look at the symptoms of deep vein thrombosis.
Although some people may not see any symptoms of deep vein thrombosis, here are the most common ones to look out for:
- Pain, swelling and tenderness in one (rarely both) of your legs.
- A heavy ache in the affected area.
- Red skin around the area - particularly at the back of your leg, below the knee.
- Warm skin in the area of the clot.
- A mild fever.
The pain in your leg may also worsen when you bend your foot upward towards your knee.
Remember that deep vein thrombosis mostly occurs in the leg, but it can happen elsewhere too. You may notice the symptoms described above in your stomach or arm, indicating a possible clot there. Similarly, DVT usually occurs in one leg but clots in both legs are possible too. If you notice any of these symptoms, then you should ask for an urgent GP appointment or call 111.
Diagnosis of Deep Vein Thrombosis
There are a few tests that doctors use to identify deep vein thrombosis. One example is the D-dimer test, which detects pieces of a blood clot that have broken down and are now loose in your bloodstream. The more fragments it detects, the more likely it is that you have a blood clot in your vein.
Other tests include an ultrasound to detect blood clots and a venogram if the previous two tests were unable to confirm a diagnosis. During a venogram, a special liquid known as contrast dye is injected into a vein in your foot. This then travels up your leg and can be detected by an X-ray - which will highlight a gap in the blood vessel where a clot is stopping the flow of blood. However, this method is much rarer nowadays, thanks to advances in ultrasound technology.
Deep Vein Thrombosis Treatment
Once you have received a positive diagnosis, treatment usually involves medicines called anticoagulants. Heparin and warfarin are common examples. These reduce the blood's ability to clot and prevent existing clots from growing. You might also hear them referred to as "blood-thinning" medicines.
Heparin & Warfarin
In most cases, doctors will prescribe heparin first, because it starts working immediately to prevent clots. This medicine is available in two different forms:
- Standard (unfractioned) - can come in an injection straight into one of your veins or via a continuous drip into a vein in your arm. It can also be given as an injection under your skin.
- Low molecular weight - Usually comes as an injection under your skin.
Both forms of heparin can cause side affects, such as bleeding, a skin rash, and the weakening of your bones if you take it for a long time. In rare cases, heparin can also cause an extreme reaction that worsens existing blood clots and can cause new clots to form.
Warfarin on the other hand is taken as a tablet. Your doctor may give you warfarin after an initial treatment of heparin, in order to prevent new clots from forming. Usually, they recommend taking warfarin for three to six months, whereas some patients will need to take it for longer, even for life. Unlike heparin, warfarin is not suitable for pregnant patients.
Patients who begin taking warfarin will have regular blood tests 2 or 3 times per week to pinpoint the correct dosage. Eventually, you will only need a blood test every 4 weeks.
Several factors can affect how warfarin works: your diet, other medicines that you're taking, and how well your liver is working. You should therefore consider the following if you're taking this medication:
- Limit your alcohol intake.
- Keep your diet consistent.
- Don't take any herbal medicine.
- Take your dose of warfarin at the same time every day.
- Don't start any other medicine without checking with your doctor.
Your doctor will almost certainly prescribe compression stockings, which you must wear every day. This is in order to improve your symptoms and prevent any further complications. You will also be advised to raise your leg whenever you're resting, as this helps to relieve the pressure in the veins and stops blood and fluid pooling in the calf itself.
When raising your leg, make sure your foot is higher than your hip. This will help the returning blood flow from your calf. Putting a cushion underneath your leg while you're lying down should help raise your leg above the level of your hip.
Without treatment, around 1 in 10 people with deep vein thrombosis will develop a pulmonary embolism. This is a very serious condition that can be life-threatening. If you are experiencing pain in your chest or upper back, you're having difficulty breathing, or you cough up blood, you should call 111 straight away. However, if you have severe breathing difficulty or your heart is beating very fast, you should call 999 or go straight to your nearest A&E.
Deep Vein Thrombosis Prevention
Furthermore, if you're planning a long-distance trip, you should take the following precautions:
- Drink plenty of water.
- Avoid taking sleeping pills as they can cause immobility.
- Take occasional short walks when possible, either up and down the train/plane aisle or at service stations.
- Wear elastic compression stockings.
- Perform simple leg exercises.
- Avoid drinking excessive amounts of alcohol as this can cause dehydration.
Preventing DVT While in Hospital
Whenever you are admitted to hospital (or due to go into hospital for surgery) you will have an assessment of your DVT risk. Certain medical treatments and surgeries can increase your risk of developing deep vein thrombosis. Therefore, your medical team will take whatever action is necessary to try and prevent clots. If you are at risk, they will likely give you compression socks and teach you some simple exercises to lower your risk.
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Editor's Note: This article was updated on 23rd March 2022 to reflect current information.