Deep vein thrombosis

Blood clots

Deep vein thrombosis occurs when a blood clot (also called thrombus) forms in one or more of the deep veins in your body, usually in your legs.

Blood clot formation is a normal process in the body that prevents you from bleeding too much when a blood vessel is injured. Sometimes, blood clots form within a blood vessel and may become lodged in veins deep inside the muscle – this is known as deep vein thrombosis (DVT).



The most common veins that are affected are those in the legs. The clot will either partially or completely block the flow of blood through the affected vein, causing swelling and discomfort. 

DVT is a serious condition because blood clots in your veins can break loose, travel through your bloodstream and lodge in your lungs, blocking blood flow. This is called pulmonary embolism (or PE) and can be fatal.

Who is at risk of developing DVT?

Many factors can increase your risk of developing DVT. The more risk factors you have, the greater your risk.

Risk factors for DVT  Description
Being inactive for long periods of time
  • Bedrest for long periods of time causes reduced blood flow  in your veins.
  • Sitting for long periods of time such as when flying, driving or at a desk.
Surgery and injury (trauma)
  • Major surgery or operation especially of the pelvis, abdomen (tummy), hip or knee, or a bone fracture. 
  • Having a catheter (tube in your vein) in a big vein such as a PICC line, central venous catheter, or port.
  • Read more about hospital-related DVT
Increased hormones (oestrogen and progestin) 
  • Birth control pills
  • Hormone replacement therapy (HRT)
Pregnancy
  • Pregnancy, including up to 6 weeks after giving birth
Medical conditions
  • Having cancer 
  • Heart failure
  • Inflammatory disorders such as lupus, rheumatoid arthritis,
    inflammatory bowel disease
  • The kidney disorder called nephrotic syndrome
Lifestyle factors
  • Being overweight or obese – this increases pressure in the veins 
  • Smoking – affects blood clotting and circulation
Other 
  • Age – although DVT can occur at any age, being over 60 years increases your risk
  • Having varicose veins
  • Genetic clotting disorder
  • If you or someone in your family has had DVT or pulmonary embolism before, you're more likely to develop DVT

What are the symptoms of DVT?

A DVT can occur in any limb but tends to occur more commonly in the leg, involving the foot, ankle, calf, or whole leg.

Signs and symptoms can include:

  • Swelling in the affected limb. Rarely, there may be swelling in both legs.
  • Pain in your leg. The pain often starts in your calf and can feel like cramping or a soreness.
  • Change of colour in the leg – bluish, purple or reddish skin colour.
  • Feeling of warmth on the skin of the painful or, swollen area.   

These symptoms may often be confused with a sprained ankle or other injury. DVT may sometimes occur without any noticeable symptoms. If you develop signs or symptoms of DVT, contact your doctor. 

How is DVT diagnosed?

To diagnose DVT, your doctor will ask you questions about your symptoms. You'll also have a physical exam to check for any areas of swelling, tenderness or discoloration on your skin. Depending on how likely you are to have a blood clot, your doctor may suggest further testing, including:

  • Ultrasound scan, which uses high-frequency sound waves to detect the presence of blood clots. This is a painless procedure.
  • Blood test – almost all people who develop severe DVT have an elevated protein in their blood called D dimer.

How is DVT treated?

The main aim of DVT treatment is to prevent the clot from getting any bigger, and from breaking loose and causing a pulmonary embolism. After that, the goal becomes reducing your chances of deep vein thrombosis happening again. Treatment usually includes a combination of medication and compression.

Medications – anticoagulants (blood thinners)

Anticoagulant medications "thin" the blood, by decreasing its ability to clot. They prevent new clots from forming and existing clots from growing larger. Common examples of anticoagulant medications are:

  • enoxaparin (also called Clexane) which is given by injection under the skin (subcutaneously)
  • warfarin which is given in tablet form
  • dabigatran which is given in capsule form.

You will require regular blood tests to check how well the anticoagulants are working and if dosage changes may be required. Anticoagulant treatment usually continued for at least 3 months to be fully effective in treating a DVT. In some cases, it may be required on a long-term basis.

Compression stockings

These are special types of stockings that are made from special elastic to give support to the lower legs, encourage circulation and help to reduce swelling. This pressure helps reduce the chances that your blood will pool and clot. These stockings are worn on your legs from your feet to about the level of your knees.

How can DVT be prevented? 

Although DVT cannot be prevented in all situations, there are a few measures you can take to lower your risk, such as:

  • Avoid sitting for long periods of time. Elevate your legs if you are sitting for moderate periods of time.
  • If you are travelling on a long journey or are bedridden in hospital there are special precautions you can take. See travel-related DVT and hospital-related DVT.
  • If you smoke, quit smoking or reduce the amount that you smoke. The nicotine causes your blood
    vessels to become smaller and the blood flow is decreased.
  • If you are overweight, aim to reduce weight. 
  • Exercise regularly. 
  • Keep hydrated – drink 6 to 8 glasses of water a day.

Learn more

Deep vein thrombosis Patient Info, UK
Deep vein thrombosis (DVT) Mayo Clinic, US

References

Deep Vein Thrombosis (Blood Clots) CDC, March 2016