Deep vein thrombosis (DVT) occurs when a blood clot, or thrombus, forms in deep-lying veins, usually in the larger lower veins of the legs.
If the clot is large, it may interfere with circulation of the area and block blood flow from the legs back to the heart. A piece of the clot (embolus) may break off and be carried through the bloodstream.
The embolus can lodge in the lungs, blocking the blood flow and causing severe damage. A pulmonary embolus (a blood clot that travels to the lungs and blocks a lung vessel) can be fatal.
Unlike the deep veins, which are located inside the leg tissues and cannot be seen, varicose veins (enlarged veins on the legs) are superficial, located just under the surface of the skin.
Although clots can develop in superficial veins, they are not usually dangerous although they are frequently tender.
DVT may occur when the blood pools in the deep veins in your legs, when there is some factor that makes your blood more likely to clot or when there is damage to the vein wall.
The blood will pool if the flow is interrupted. This may happen because there is compression of the vessel so the vein is narrower, or if the normal ‘muscle pump’ of the leg is not pumping blood back to the heart.
For example, when you are bedridden (after surgery) or when you sit still for prolonged periods (such as during a long aeroplane flight) your blood tends to pool.
Blood pools in the larger veins of your legs and clots may form. Injury, certain kinds of major illness and some medications also increase the tendency for blood to clot. (See risk factors below)
Deep-vein thrombosis occurs in approximately two out of 1 000 people and is most commonly seen in adults over age 60. Conditions and circumstances that increase your risk of developing DVT include:
- Recent surgery or trauma, especially hip, leg or knee surgery; gynaecological surgery or heart surgery. Hip and knee surgery may lead to damage of the vessel wall as well as immobility.
- Fractures of the hip, femur (thigh bone) or lower leg
- Being bedridden or in a wheelchair
- Heart failure, as the blood flow back to the heart is slower than normal
- Heart attack
- Cancerous tumours may compress the vein if they are big or may secrete a substance that makes the blood more likely to clot
- Pregnancy, using oral contraceptives or taking oestrogen
- Older age (over 60)
- Previous DVT
- Childbirth within the previous six months
- Blood disorders that result in increased tendency of the blood to clot (hypercoagulability) for example antiphospholipid syndrome or atithrombin III deficiency. Polycythemia vera (a disease in which there is an excess of red blood cells) is another disorder that increases risk.
Symptoms and signs
About half of people with deep-vein thrombosis have no symptoms until a clot blocks a major vein. Symptoms typically occur in one leg only and may include:
- Swelling in the calf, ankle, foot or thigh
- Increased warmth of the leg
- Pain which is usually located in the calf or behind the knee and may worsen on standing or walking. Resting with the affected leg raised often relieves the pain.
- Leg cramps at night
- The affected skin may be slightly redder than normal. If there is a bluish tinge it means there is a major blockage and the patient should seek medical help immediately
- Joint pain
- Positive Homan’s sign is when you experience sharp pain in your calf when your foot is flexed upward with your knee slightly bent. This may be an early sign of DVT in the calf.
- Slightly elevated temperature (37.5C)
- Cellulitis. This is an infection of the soft tissue which is caused by a bacteria and needs antibiotics. The skin is usually warm and you may have a temperature.
- Superficial vein thrombosis.
- Injury to the leg.
Your doctor will take your medical history and perform a physical examination. However, further tests are needed to confirm the diagnosis of deep-vein thrombosis because the symptoms are often similar to those of other conditions. Common tests include:
- Duplex doppler. This is a combination of ultrasound (which uses high-frequency sound waves to create an image of the leg veins) and a flow ‘probe’ which shows the direction of the flow of the blood in the veins. This combination will show any blockage in the veins.
- Contrast venography. This involves injecting a substance into the veins that shows up on X-ray.
Blood clots are sometimes discovered on performing a CT (computerised tomography) scan of the pelvis.
A sample of your blood may also be sent to the laboratory to test for conditions that cause increased blood clotting tendency.
Treatment usually requires hospitalisation and bedrest, at least initially. However, prolonged sitting in one position is to be avoided.
A combination of heparin and warfarin (anticoagulants which 'thin' the blood in order to prevent further clots) is used at first. The heparin helps the warfarin to start working. The heparin starts working within a few hours but has to be injected. It used to be given by drip but is now injected into the fat once a day. Regular blood tests tell your doctor when these drugs are working correctly.
Once the drugs have started to work, the heparin is stopped and the warfarin is continued on its own. This is usually continued for up to six months. Regular blood tests are used to indicate the correct dose of warfarin.
This treatment is aimed at relieving symptoms and preventing the clot from embolising to other areas of the body such as the lungs, heart or brain.
If the clot is so big it means that the survival of the leg is in doubt, you may be given thrombolytic agents. These are drugs that are injected into the blood to break down the blood clot. As they can cause unwanted bleeding, they are not used routinely.
Leg compression devices are often used to prevent DVT while you are in hospital. The leg may be elevated to reduce swelling. Warm, moist heat can be applied to the affected area to relieve pain.
In rare cases, the clot may need to be surgically removed.
After you are discharged from hospital, you will continue to take oral anticoagulants or antiplatelet medications for some time. You usually need to take warfarin for at least six months after you develop DVT.
People who have a tendency to form blood clots more easily than others may have to take anticoagulants for the rest of their lives. Warm compresses may also be continued. It is important to avoid prolonged sitting or standing in one position.
It is vital to go for regular blood checks while you are on these drugs to ensure your blood doesn’t become too thin.
Most deep-vein clots resolve without difficulty. However, the complications that may occur are life- threatening and include:
- Pulmonary embolus
- The deep veins in the leg may become scarred after a blood clot. This means they may close and the blood is forced to flow back to the heart through the superficial veins. The superficial veins on the leg may become dilated (varicose veins) or the skin may become ulcerated (venous ulcer).
- Certain types of cancer predispose to deep-vein thrombosis or pulmonary embolus. This is probably because even a small tumour can make blood clot more easily. Occasionally the tumour may cause compression of the vein which causes the blood to pool in the leg. A blood clot, particularly if it is in a strange part of the body such as the arm, can sometimes be the first sign of cancer. However, most DVT is not related to cancer.
General health measures (taking regular exercise, giving up smoking and controlling your weight) can help lower your overall risk for deep-vein thrombosis.
For people who have had DVT or are at risk of developing of DVT, the following prevention measures are recommended:
- Avoid prolonged bedrest or immobility of the legs. Leg exercises help to prevent pooling of blood in the legs. Walking as soon as possible after surgery will help lower your risk of DVT. If you are unable to exercise, your caregiver should massage your legs and perform passive exercises on them within their range of motion.
- Ask your doctor or pharmacist about special supportive elastic stockings. Ensure the stockings fit smoothly and firmly but are not too tight in any one area as this can block blood flow. Remove them once a day to wash them and to check the skin for discoloration or irritation.
- Keep your legs elevated when you are lying or sitting down to promote the return of blood through the leg veins.
Similar anticoagulant medications used to treat DVT can also be used as a preventive measure in people with a high risk of developing the condition. If you use anticoagulants:
- Take the correct amount of medication at the right time each day.
- Regular blood tests will be needed to monitor how fast your blood clots. Follow instructions as to when to have these tests.
- Wear a Medic-Alert bracelet showing which drugs you are taking.
- Consult your doctor before taking any new medications, including non-prescription drugs. Most medicines and all antibiotics can interfere with the effects of anticoagulants.
- Avoid aspirin and other non-steroidal anti-inflammatories such as ibuprofen, unless specifically prescribed by your doctor. Adding aspirin to anticlotting drugs can increase the risk of bleeding.
- Tell your other health care providers, such as your dentist, that you are taking anticoagulants.
- Call your doctor immediately if you have any of the following symptoms:
- severe headaches
- severe stomach pain
- increased weakness
- red or brown urine
- bruises that increase in size without further injury
- red or black bowel movements
- cuts that do not stop bleeding
- coughing up blood
- any unusual or unexplained bleeding.
When to call the doctor
Call your doctor if you experience symptoms that suggest deep-vein thrombosis (see symptoms and signs).
If a person with DVT shows severe symptoms such as chest pain, difficulty breathing, fainting or loss of consciousness, go to an emergency room or call the local emergency number.
Reviewed by Dr K. Michalowski MD FCS(SA) FRCS.
DVT a danger during travel
Image: Blausen.com staff. "Blausen gallery 2014". Wikiversity Journal of Medicine. DOI:10.15347/wjm/2014.010. ISSN 20018762. - Own work, Creative Commons 3.0