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What is thrombosis?
This article describes the different types of thrombosis and how they form.

Thrombosis - a serious issue
Blood clotting
Types of blood clot
What is deep-vein thrombosis (DVT)?
What is pulmonary embolism (PE)?
What is superficial thrombosis?
What is the post-thrombotic syndrome?

Thrombosis - a serious issue
The development of blood clots (a process called thrombosis) within blood vessels can lead to serious complications or death if it is not recognized or treated effectively.

Thrombosis can affect:

• sick patients
• hospitalized patients
• patients undergoing major surgery
• patients with serious medical conditions (e.g. stroke, heart disease or cancer)

However, people without other medical problems can also be affected, such as the elderly or pregnant women.

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Blood clotting

Blood clotting is a natural, protective mechanism that is triggered by the body in response to a cut or wound. It is essential to prevent you from bleeding excessively. It also prevents your wounds from becoming infected by germs. The blood-clotting process is a complex sequence of chemical reactions. Your blood contains blood-clotting proteins, anticlotting proteins and minute cell fragments called platelets, all of which are important in this process. However, blood clotting can malfunction, and the result can be thrombosis, the formation of a harmful blood clot (or thrombus). This can be caused by a narrow, blocked or damaged blood vessel (an artery or a vein) as a result of poor circulation, inactivity (e.g. prolonged bedrest) or severe infection. Blood clots can either partially or completely block the flow of blood. Some people are born with factors that make clots more likely to form in their blood vessels, and others may be born with defects in natural, vital blood thinning substances called anticlotting proteins, and are therefore more likely to develop blood clots.

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Types of blood clot
There are two types of blood clot: arterial blood clots form in the arteries and venous clots form in the veins.

Arteries are blood vessels with thick muscular walls that assist in the maintenance of blood pressure. Arteries carry the blood under high pressure away from the heart. Arterial clots are white and are made up mainly of platelets. Arterial clots are the major cause of heart attack and stroke. 
 
Veins are blood vessels with thin fibrous walls. Veins carry blood at low pressure from the tissues of the body back to the heart. In the legs they have one-way valves to prevent the blood from flowing backwards.  
   
Venous clots are red and are made up mainly of sticky threads of fibrin, which is formed from blood clotting proteins. Examples of venous clots are deep-vein thrombosis (DVT) and pulmonary embolism (PE).

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What is deep-vein thrombosis (DVT)? 

Deep-vein thrombosis is the formation of a blood clot (thrombus) within one of the large, deep veins of the body. It usually occurs in the deep veins of the calf, thigh, knee or pelvis. DVT is not a rare condition, but it is difficult to detect in many patients. Symptoms of DVT include varicose veins swelling of the leg tenderness or pain redness in the affected limb Deep-vein thrombosis itself is not life-threatening, but will require you to visit hospital and can occasionally lead to serious problems, such as high blood pressure in the veins (venous hypertension), leg pain, skin ulceration, and impaired mobility. It is possible for patients with DVT to suffer from recurrent episodes in the course of their lives.

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What is pulmonary embolism (PE)? 
 Of those patients who have deep-vein thrombosis (DVT) but are not treated for it, about 10-20% develop PE. PE is the most serious complication of DVT, and occurs when a blood clot in the vein breaks up into smaller pieces called emboli. These pieces of clot can be carried in the blood to the lungs where they can obstruct the blood vessels and reduce or prevent the flow of blood to the lungs. If PE is left untreated, you are at a higher risk of related problems such as heart failure or sudden death. Patients who experience recurrent PE may develop high blood pressure in the blood vessels that supply the lungs (pulmonary hypertension).

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What is superficial thrombosis? 
 As well as having a system of deep veins within the muscles of your body, you also have a system of veins that is close to the surface of your skin (the superficial system). You will be able to see these veins more clearly when you exercise. Superficial thrombosis is the development of blood clots in the veins close to the skin surface. It is very different to deep-vein thrombosis (DVT) and is less serious, although it can cause in the area of the vein. If you suffer from this problem, you could be treated with anti-inflammatory medications [medication such as nonsteroidal anti-inflammatory drugs (NSAIDs) to reduce the swelling] and occasionally with antithrombotic agents. If you are in pain, your physician may prescribe bedrest during the initial treatment; although you are likely to be encouraged to become mobile as soon as possible. You also need to receive compression therapy (such as wearing elastic stockings), you may receive heat treatment as pain relief, and you need to stay mobile.

• pain
• swelling
• redness

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Post-thrombotic syndrome is caused by damage to the one-way valves in the veins, which leads to high blood pressure in these blood vessels. Post-thrombotic syndrome is the name used to describe the long-lasting swelling, redness, pain and, in severe cases, ulceration that can sometimes occur after an episode of DVT. Some patients who have venous thrombosis can develop post-thrombotic syndrome. The pain is relieved by rest and raising the affected limb. The swelling may never disappear, or it may return a few years later. Post-thrombotic syndrome is sometimes difficult to diagnose because it looks like DVT. If you are likely to have post-thrombotic syndrome, it usually develops within 2 years of your DVT. Patients who have had DVT are normally given advice about how to prevent the development of post-thrombotic syndrome.

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