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| Are you at risk? |
| This article explains the different risk factors for thrombosis and advises how to reduce your risk. |
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The risk factors for thrombosis
What can you do to decrease your risk?
What may your physician recommend?
There are several factors, known as risk factors, that increase your chances of developing thrombosis. You are more likely to be at risk of deep-vein thrombosis (DVT) if you have injured the deep veins in your limbs (e.g. if you have broken bones, severe muscle injury or have undergone surgery); slowing of blood flow through your veins (e.g. because of immobilization) or a condition that increases the tendency of your blood to clot (e.g. thrombophilia). Many patients have a combination of these risk factors and are at high risk.
The risk factors for thrombosis
- major operations
- trauma (fractures)
- medical conditions
- cancer and its treatment
- stroke or paralysis
- previous DVT
- immobility/lack of movement
- severe varicose veins
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- increasing age
- pregnancy
- some oral contraceptives
- being very overweight
- smoking
- thrombophilia
- long journeys
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What can you do to decrease your risk?
Major operations
Major operations increase the risk of deep-vein thrombosis, particularly if the operation involves the lower half of the body (abdomen, pelvis and legs). During pelvis, hip or knee surgery, for example, the vein wall may be injured and this can promote thrombosis. Other factors that may increase the risk of DVT include the type of surgical procedure used, the duration of the operation, the type of anesthetic, whether a long-term venous catheter (a tube used to introduce fluid into the veins) was required, and how long you have to remain in bed after the operation.
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Trauma (fractures)
Trauma such as a bone break or a severe muscle injury is the most common cause of injury to a vein. This injury could cause narrowing or blocking of the vein, which allows the blood to clot more easily. This is of particular concern if you have a fracture of the pelvis, hip or leg. Your risk of deep-vein thrombosis will be increased if you have to wear a cast to protect a fractured leg because your leg is immobilized.
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Medical conditions
Certain medical conditions are associated with increased risk of deep-vein thrombosis (DVT). These include heart attack, varicose veins and inflammatory diseases. Poor circulation and immobility during prolonged bedrest are two important factors that increase the risk of DVT in patients who have these medical conditions.
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Cancer and its treatment
Patients with cancer are at risk of thrombosis because their blood has an increased tendency to clot. This risk is further increased by cancer therapy. Chemotherapy (cancer-killing chemicals) and radiation therapy (cancer-killing X rays) can cause the veins to become narrow or blocked, which further increases the likelihood of blood clotting.
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Stroke or paralysis
Stroke increases the risk of developing thrombosis because it can result in general immobility. Paralyzed limbs as a result of a stroke or spinal cord injury are at particular risk of thrombosis.
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Previous deep-vein thrombosis
If you have already had deep-vein thrombosis (DVT), you are more likely to get it again than someone who has never had this condition. This may be because you inherited some factors from your parents that make you susceptible to DVT, or because your previous episode of DVT altered the structure of your veins in some way to make another episode of DVT more likely.
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Immobility/lack of movement
When you are active, movement of your leg muscles helps to keep the blood flowing through your deep veins. If you are immobilized for a long time, for example you have to stay in bed after an operation or accident, the blood flow in your veins will be slower. This increases the chances of blood clots forming in the veins.
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Severe varicose veins
Varicose veins are swollen and twisted veins that look blue and are close to the surface of the skin. Varicose veins are most often seen on the insides of the legs and at the back of the calf. Severe varicose veins can cause symptoms such as aching, throbbing or tenderness, and medical problems such as clotting or inflammation of the varicose veins. If you have varicose veins causing symptoms or medical problems, you should consult your physician.
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Increasing age
Deep-vein thrombosis (DVT) is more common in the elderly than in younger people. The risk of DVT gets higher with age. From about the age of 40 years the risk increases significantly. It is much higher in people over 50 years old, and increases further in people over 60 and over 70. This higher risk may be because older people are more likely to have other risk factors for thrombosis (e.g. restricted movement or cancer) and are also more likely to require an operation.
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Pregnancy
 During pregnancy the blood has a natural increased tendency to clot to prevent excessive bleeding during childbirth. Pregnant women are therefore at greater risk of deep-vein thrombosis (DVT) than nonpregnant women. Cesarean delivery increases the risk of DVT. Although it is very uncommon for a pregnant woman to experience a DVT, thrombosis is still an important factor in miscarriage and maternal death.
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Some oral contraceptives (estrogens) 
Estrogens are hormones that are included in some oral contraceptive pills and, in much smaller amounts, in hormone replacement therapy (HRT) for women during and after the menopause. These hormones can slightly increase the risk of deep-vein thrombosis (DVT) by making the blood more susceptible to clotting. Some oral contraceptives (e.g. progesterone-only pills) do not contain estrogen and do not increase your risk of DVT. You should not stop taking your oral contraceptive without first consulting with your physician.
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Being very overweight
If you are seriously overweight, or obese, you are at greater risk of developing deep-vein thrombosis (DVT). Your weight is an important risk factor, particularly if you also have other risk factors. For example, seriously overweight patients are more likely to develop DVT after a major operation than patients who are not overweight.
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 Smoking
Although more scientific research is necessary, it may be that smokers are at greater risk of deep-vein thrombosis (DVT) than nonsmokers. If you are a smoker, and you are also obese, your risk of DVT is increased still further.
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Thrombophilia
The term thrombophilia describes a high tendency for blood clotting. This can be the result of factors inherited at birth, so if people in your family suffer from thrombosis, there is a chance that your blood may also have a relatively high tendency to clot. Some people are born without components that dissolve blood clots or without factors that set these components in motion. Others are born with defective enzymes that lead to increased blood clotting.
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Long journeys
Long-haul flights or long car, bus or train journeys are associated with increased risk of deep-vein thrombosis because you have to sit still for long periods of time in a limited space. The risk is even greater if you are dehydrated and sit with your legs crossed because this restricts the flow of blood to your lower leg.
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What can you do to decrease your risk?
If you are at particular risk of thrombosis, your physician will probably recommend certain actions that you can take to reduce your risk, including adapting your behavior and habits or taking medication. If you have any concerns about your health and risk of thrombosis, or have any questions about the information or treatment you have been given, you must consult your family physician. There are several actions you can take to decrease your risk of developing thrombosis. Alert your physician of previous deep-vein thrombosis (DVT) You should alert your physician of any previous DVT if you:
- are about to undergo major surgery
- suffer a bone fracture
- are diagnosed with a medical condition, such as heart disease or cancer
- are prescribed prolonged bedrest or immobility
- are pregnant
- are in any other situation that increases your risk of DVT
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Estrogens, obesity and smoking
If you are seriously overweight, are taking estrogen in an oral contraceptive and are a smoker, you may have a greater risk of DVT than if only one of these factors applied. If you stop smoking and lose some weight, you will greatly reduce your overall risk of developing DVT. You may not need to stop taking your oral contraceptive, and should not do so without first consulting your physician.
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Long journeys
The risk of DVT during long journeys can be reduced by not crossing your legs; periodically getting up and walking around (if possible); and performing leg exercises while seated, such as squeezing your calf muscles, pointing and flexing your feet and wiggling your toes. The risk of DVT can also be lessened if you avoid alcohol and drink plenty of water, in order to ensure that you are not dehydrated.
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Improving your circulation
Make a habit of sitting with your legs together rather than crossed and perform leg exercises as often as possible while seated (e.g. squeezing your calf muscles, pointing and flexing your feet and wiggling your toes). Keep mobile as much as possible, for example, try to walk around for a few minutes every hour. Avoid wearing tight clothing that could restrict the flow of blood in your legs or arms. If your legs feel swollen and heavy at any time, have a lie-down with your feet higher than the rest of your body. This should decrease the swelling and discomfort.
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What may your physician recommend?
If your physician considers you to be at increased risk of thrombosis and you are about to undergo major surgery or are pregnant, for example, he/she may recommend treatment.
There are a variety of medications and device options available to prevent or treat thrombosis. Your doctor will only recommend those treatment options that he/she believes are appropriate for you and will benefit you.
Possible options for prevention or treatment include:
- mechanical devices (e.g. elastic stockings, intermittent pneumatic compression)
- low-molecular-weight heparin (LMWH)
- unfractionated heparin (UFH)
- low-dose aspirin
- oral anticoagulants (e.g. warfarin)
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