Deep vein thrombosis (DVT): a blood clot in the leg

Causes and who gets it

A clot forms when blood flow slows down, when the wall of a vein is damaged, or when the blood clots too easily. Often several factors are present together; sometimes no clear cause is found. The main risk factors are:

• Not moving: bed rest, a plaster cast, paralysis, sitting for long periods
• Surgery, especially hip, knee and pelvic surgery; the risk is highest in the first 3 months
• A hospital stay, a broken bone or a serious injury
• Cancer and cancer treatments
• Pregnancy and the period after giving birth
• Birth control that contains estrogen, and hormone therapy for menopause (HRT)
• A previous clot, or a family history of clots
• Thrombophilia (a tendency of the blood to clot easily, either inherited or developed later in life)
• Older age: after age 40, the risk roughly doubles every 10 years
• Excess weight and smoking
• Journeys of more than 4 hours
• Heart failure, kidney disease and inflammatory bowel disease; long-term catheters (thin tubes) in a vein

Symptoms

Symptoms usually appear in one leg, in the calf or the thigh:

• Throbbing pain, or tenderness that gets worse when touched
• Swelling
• Warmth in the painful area
• Red, purplish or darkened skin; on brown or black skin this change is harder to notice
• Veins that look more prominent

Less often, a clot forms in the arm and causes the same symptoms there; this is more common in people who have a long-term catheter in a vein. DVT does not always cause symptoms. Sometimes there are no complaints at all until a pulmonary embolism develops.

Diagnosis and tests

Your doctor will ask about your symptoms, your risk factors and your medicines, examine your leg, and look for other causes of the swelling.

• Clinical probability assessment: Your doctor scores how likely DVT is based on your findings and risk factors; the order of tests is decided based on this.
• D-dimer: A blood test that measures a fragment that enters the blood as a clot breaks down. When the probability is low, a normal result largely rules out DVT. A high result does not on its own mean there is a clot; it can also be raised in pregnancy, after recent surgery and in older age.
• Compression (Doppler) ultrasound: Uses sound waves to show the veins in the leg and the blood flow in them. It is the preferred first imaging test when DVT is suspected and is often enough to make the diagnosis.

If the probability is high and the ultrasound is normal but the D-dimer is high, the ultrasound may be repeated 6–8 days later. A CT scan or MRI may be ordered for veins in the pelvis or abdomen. A blood thinner may be started while you wait for results; if a clot is found, its cause is also looked for.

Treatment approach

The main treatment for DVT is blood-thinning medicines (anticoagulants). These medicines do not dissolve the clot directly; they reduce the risk of pulmonary embolism by stopping the clot from growing and new clots from forming.

• Medicine: Given as an injection, a tablet or through a vein (IV). The choice depends on your kidney and liver health, your bleeding risk, pregnancy and your other medicines. Many people are treated at home.
• Duration: This varies from person to person; whether the clot was linked to a temporary cause, and the risks of another clot and of bleeding, are weighed together. Sometimes treatment is lifelong.
• Clot-dissolving (thrombolytic) medicine: Rarely, for large clots with severe symptoms, and preferably delivered into the clot through a catheter; the bleeding risk is high.
• Filter: In some people who cannot take blood thinners, a filter may be placed in the main vein (the vena cava) to stop the clot from traveling to the lungs; it is often temporary.

Compression stockings do not treat the clot; they may be recommended to ease pain and swelling that continue after DVT. NICE, the national guideline body in England, however, does not recommend giving stockings to prevent long-term leg problems or a new clot. Ask your doctor whether you need stockings. Do not stop your medicine on your own.

Everyday life and follow-up

The most important side effect of blood thinners is bleeding. If you notice any of the following, contact your doctor or go to the emergency department right away and tell them which medicine you take; for heavy bleeding or loss of consciousness, call 112 (in Türkiye) or your local emergency number:

• Long-lasting nosebleeds or bleeding gums, heavier periods
• Large bruises that appear without an injury
• Red or brown urine; red or tar-colored stools
• Coughing up or vomiting blood
• A severe headache, or changes in balance or consciousness

In daily life:

• Once treatment has started and your symptoms ease, walk; keep your leg raised when sitting.
• Ask before starting any new medicine, herbal product or vitamin. Some painkillers, such as aspirin and medicines for rheumatism, increase bleeding. If you take warfarin, see our articles on vitamin K and INR.
• Keep alcohol limited.
• Tell your dentist and all your doctors that you take a blood thinner; carry a card that shows this.
• The NHS recommends postponing flights or long journeys for at least 2 weeks after treatment starts; travel advice is in our related articles.

Some people are left with long-lasting swelling, pain or color change in the leg (post-thrombotic syndrome). Tell your doctor about this.

Pregnancy, children and special situations

Pregnancy and after birth: During pregnancy and right after giving birth, the risk of a clot increases more than 5 times. The risk is especially high in the first 6 weeks after birth and can last up to 3 months; a cesarean section also increases the risk. In pregnancy, DVT is usually treated with blood thinners given by injection. Some tablet blood thinners are not recommended during pregnancy or breastfeeding; if you take a blood thinner, talk to your doctor about your pregnancy plans in advance.

Children: DVT is very rare in children in the general population. In children staying in hospital, however, the risk is 100 to 1,000 times higher; most clots are linked to catheters placed in a vein. In children, treatment is usually started in hospital.

In Türkiye

If you have signs of a pulmonary embolism, call 112. Because an ultrasound is needed to diagnose DVT, if you have DVT symptoms you can go the same day to a hospital emergency department, or to an internal medicine or cardiovascular surgery outpatient clinic. If there is no danger to life, your family doctor (aile hekimi) can also do the first assessment.

The 2021 national guideline of three societies in cardiovascular surgery and phlebology recommends color Doppler ultrasound as the first test when DVT is suspected, and supports home treatment for suitable patients. The Türk Hematoloji Derneği (Turkish Society of Hematology) has a patient guide on venous thrombosis. If the cause of a clot is unclear, or if clots keep coming back, you may be referred to a hematologist.

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