Blood clotting is a natural process in which blood cells and fibrin strands rapidly form a clump to stop bleeding after a blood vessel has been injured. Eventually the clot will form a protective scab over a wounded blood vessel, allowing it to heal. If the body did not have the ability to form blood clots, people would bleed to death after even a minor cut.

Sometimes, however, blood clots form even when a person has not been injured. Although most blood clots tend to dissolve on their own with no long-term problems, there are situations in which blood clots can cause medical problems. Blood clots become dangerous when they block blood flow through an artery or vein.

When a blood clot blocks blood flow to an artery in the heart or brain, a heart attack or stroke may result. Blood clots can also block veins and arteries throughout the body, causing diseases that range from varicose veins to a life-threatening pulmonary embolism.

Physicians treat blood clots with a variety of methods. Medications such as anticoagulants (which help prevent blood clots) and clot busters (which help to dissolve blood clots) are prescribed to prevent and treat blood clots. In more serious situations, physicians might opt for a catheter-based procedure, which uses a long, thin tube called a catheter, or even surgery to remove the clot (thrombectomy). In addition, devices may be implanted into certain blood vessels to catch blood clots before they can cause serious damage.

Blood clots are formed by the process of coagulation - the blood’s natural tendency to clump and plug an injured blood vessel. Blood clots are made of blood cells and fibrin strands. They serve a valuable function in wound healing and stopping the flow of blood after an injury.

For example, when a person is cut, blood flows from the injured blood vessel for a short period. However, the clotting process begins almost immediately. During this process, blood platelets first gather at the site of the injury and form a loose plug. These platelets release a number of chemicals that enhance and promote blood clotting. Once the loose platelet plug is in place, a mesh of fibrin forms to create a stronger blood clot. This blood clot will remain in place as the tissue injury heals. After it heals, still other chemicals are responsible for dissolving the clot. This process of forming and dissolving blood clots is called hemostasis.

Blood clots are rarely dangerous on their own. As part of the body’s natural healing mechanism, clots that have formed for whatever reason are usually dissolved (lysis) and reabsorbed by the body without danger or need for intervention.

They can be dangerous, however, when they form within arteries and veins and obstruct the normal flow of blood within the body. Dangerous blood clots can form after surgery or in response to traumatic injury, such as auto accidents. 

They can also form as a result of the gradual buildup of plaque within an artery (e.g., atherosclerosis) or other diseases. Blood clots can form in any vein or artery in the body, including the coronary arteries that supply the heart with blood, the veins in the legs and the arteries that supply the brain with blood (e.g., carotid arteries).

A blood clot that forms in a location where it partially blocks a vein or artery is known as a thrombus. In some cases, a blood clot breaks off from the site it was created and travels through the bloodstream until it becomes lodged in a smaller blood vessel, blocking the blood supply. This is known as an embolus.

A blood clot can be life-threatening if it either forms or becomes lodged within any of the following arteries:

• The pulmonary artery, which travels from the heart to the lungs. Blockage in this artery is called a pulmonary embolism and may result in damage to the lung and, in some cases, death. These may be caused by an abnormal heart rhythm called atrial fibrillation or by a peripheral venous disorder in the deep veins of the legs (e.g., deep vein thrombosis).
  
  
• One of the coronary arteries, which are located on the surface of the heart and supply the heart muscle with fresh, oxygen-rich blood. Blockage of any of the coronary arteries could trigger a heart attack. Blood clots usually form in this circumstance in response to plaque rupture, which occurs when a plaque deposit on the inner wall of a coronary artery fractures, triggering the clotting process. 
  
  
• The carotid arteries, which lie in the neck and supply the brain with oxygen-rich blood. Blockage could trigger a stroke or a mini-stroke (transient ischemic attack).

  

• The femoral artery in the leg. Blockage could cause pain (claudication), lack of color in that area and weakness. If left untreated, it could result in tissue death (necrosis) and infection (gangrene).
  
  
• An artery in the abdomen. Blockage could cause pain, vomiting and/or diarrhea.

A blood clot that forms in the veins (a venous blood clot) is considered a peripheral venous disorder. These may not be life-threatening, but can result in pain and discomfort or, in some cases, serious medical conditions. Peripheral venous disorders include:

• Thrombophlebitis. An obstructing blood clot has formed, causing the surrounding vein to become inflamed (phlebitis). If the blood clot formed in a superficial vein near the surface of the skin, it is called superficial vein thrombosis. If the blood clot formed in a deeper vein, it is called deep vein thrombosis (DVT). Deep vein thrombosis is a major risk factor for pulmonary embolism. This is because the clot may break off (embolize), travel through the return circulation, pass through the right side of the heart and into the lungs, where it may cause an obstruction.
  
  
• Varicose veins. A blood clot can damage the valves within a vein. The valves are responsible for keeping blood flowing smoothly in the right direction, which is particularly important when the veins are counteracting the effects of gravity to bring oxygen–poor blood from the legs to the heart. The valves close between heartbeats to keep blood from flowing backward in the wrong direction (regurgitation). Leaky or damaged valves can cause blood to pool in the legs, resulting in swollen, varicose veins.



• Thrombotic thrombocytopenic purpura (TTP). A condition in which a lack of platelets can lead to the formation of small blood clots throughout the body. It can cause widespread damage to many organs.

There are many other conditions related to blood clots, and their names usually refer to the area of the body where the clot occurs. Coronary thrombosis, for example, is a blood clot in one of the coronary arteries. Mesenteric venous thrombosis is a blood clot in the mesenteric vein (either of two veins draining the intestine), and retinal vein occlusion refers to a blood clot in a vein of the eye.

Blood clots may form for various reasons. Severe trauma, such as from an auto accident, may cause internal blood clotting. Blood clots may also be created during surgery. For example, some side effects of open-heart surgery may be caused by tiny blood clots that form during use of the heart-lung machine (microembolization).

Blood clots may also be formed by or in association with: 

• Atherosclerosis
  
  
• Heart attack or stroke
  
  
• Valvular heart disease
  
  
• Heart failure
  
  
• Infection
  
  
• Cancer
  
  
• Autoimmune disorders (e.g., lupus or rheumatoid arthritis)
  
  
• Bleeding disorders (e.g., hemophilia)
  
  
• Inflammatory bowel disease (e.g., ulcerative colitis and Crohn's disease)
  
  
• History of varicose veins or other vascular conditions
  
  
• Pregnancy
  
  
• High blood pressure (hypertension)
  
  
• Thrombocythemia (in which greater numbers of platelets are produced)
  
  
• Atrial fibrillation

In addition, there are a number of risk factors that can increase the chances of developing a blood clot. These risk factors include:

• Smoking
  
  
• Elevated levels of homocysteine (homocysteinemia), which may be treated with diet and folic acid supplements
  
  
• Obesity (body mass index greater than 30)
  
  
• Prolonged lack of exercise
  
  
• Use of contraceptive pill or patch 
  
  
• Advanced age
  
  
• Genetic factors (e.g., inheriting a tendency to develop deep vein thrombosis)
  
  
• Sitting or laying in one position for a prolonged period of time
  
  
• Having a mechanical heart valve
  
  
• Hypercoagulable state, where genetic (e.g., Factor V Leiden) or acquired (e.g., trauma, pregnancy, Heart failure) factors affect blood clotting due to abnormal levels of blood-clotting proteins

The symptoms of a blood clot depend on where the blood clot is located in the body, as shown below:

Diagnosis of a blood clot begins with a medical history and physical examination. If a clot is suspected, a number of tests can be used to confirm the diagnosis, including:

• Doppler ultrasound. Imaging technology that uses sound and/or motion waves to produce visual images of the shape and outline of various blood vessels and organs in the body (e.g., the heart), as well as any obstructions to blood flow.
  
  
• CAT scan (computed axial tomography). A test that uses a series of x-rays taken from various angles to produce a computerized three-dimensional image of a body structure. A special dye (contrast medium) is sometimes injected prior to imaging.
  
  
• MRI (magnetic resonance imaging). A noninvasive or minimally invasive test that uses magnetic fields to produce high-resolution cross-sectional or three-dimensional visual images of the targeted area. Often, a magnetic resonance angiogram (MRA) is also done after the injection of a dye to view blood flow through the coronary arteries or carotid arteries.

Physicians may also order a venogram to assess for a blood clot in a vein. This diagnostic test involves the use of a special dye (contrast medium) that is injected into the vein of the affected area prior to an x-ray. The resulting film reveals the shape, size and composition of the vein, as well as any obstructions to blood flow. If this test is performed on an artery, it is known as an angiogram (e.g., a pulmonary angiogram). With the advent of high-resolution, noninvasive imaging, however, angiograms are usually not needed.

The treatment options for a blood clot depend on whether the clot has formed in a vein or an artery and caused a heart attack or stroke. In emergencies, thrombolytic medications (clot busters) may be used to dissolve the blood clot. These medications are administered intravenously (I.V.) to carefully selected patients according to a rigid protocol. To be fully effective, they must be given at least within one hour of the heart attack or within three hours of the stroke.

Thrombolytics are usually used with large clots that are causing severe, life-threatening symptoms. They can cause sudden bleeding and may not be suitable for all patients.

More invasive procedures may also be an option. For example, catheter-directed thrombolysis may be used, in which a catheter delivers thrombolytic enzymes directly to the blood clot. During this procedure, higher concentrations of enzymes can be used and there may be fewer side effects than when the enzymes are given intravenously.

Thrombolytic treatment is usually followed by treatment with anticoagulants to prevent additional blood clots from forming. Anticoagulants may also be prescribed to patients who have a high risk of developing a blood clot.  

Researchers are also working on various catheter-based procedures to quickly treat stroke. One procedure involves using a tiny “corkscrew” device that quickly reverses the damage caused by the stroke. This device is guided to the location of the blood clot, where it retrieves and removes the obstruction. Other emergency methods include a catheter-directed device that may be able to break up and suck out a soft clot or “scoop” out a hard clot from an artery, reducing the risk of complications. These new therapies may someday be available to patients who cannot tolerate clot-busting drugs.

If a blood clot forms in a leg vein (deep vein thrombosis), there is some risk that a pulmonary embolism will develop. A pulmonary embolism is a potentially life-threatening event in which a blood clot breaks off from its original location, travels through the bloodstream and lodges in one of the blood vessels of the lungs.

To prevent a pulmonary embolism, existing blood clots in the legs can usually be treated with a combination of heat, painkilling medications, thrombolytics, anticoagulants and elevation/bandaging of the affected area to reduce swelling. The approach will depend on the size of the clot and the severity of any existing symptoms.

If patients do not respond to anticoagulants, physicians may opt for a procedure using a catheter tipped with a special device called a vena cava filter. The vena cava filter is implanted in the large vein that carries blood from the legs to the heart and lungs, the vena cava. The vena cava filter is a device that catches blood clots in the vein before they are allowed to reach the lungs.

There are some risks associated with vena cava filters, including breakdown of the filter over time and blood clots caused by the filter itself. Researchers are working on developing vena cava filters that can be retrieved after the threat of pulmonary embolism has passed.

Studies have also confirmed that long-term therapy with low-dose anticoagulant drugs helps prevent the recurrence of blood clots among those with a history of deep vein thrombosis or pulmonary embolism.

Each patient’s treatment approach will depend on the location of the clot, its size and the patient’s general health.

Prevention strategies are particularly important among people who are prone to blood clots. People who are prone to developing blood clots in an artery include those with mitral valve prolapse, enlarged heart, atrial fibrillation or heart failure. The best strategies for preventing blood clots in an artery are to exercise regularly to promote good circulation, to treat other heart-related medical conditions, and to take antiplatelet drugs or anticoagulants as prescribed by a physician.

People who are prone to developing blood clots in a vein include those with varicose veins, obesity, chronic heart failure or habits of staying in one position for long periods of time. During prolonged travel (e.g., by air, bus, train or car), it is important to get up and walk around. If this is not practical, individuals should try to perform leg exercises while seated or standing. If traveling by car, one should try to make frequent rest stops to move the legs. Compression stockings (that reach the waist) are helpful in reducing swelling and improving venous circulation, and may help prevent blood clots. For patients with a history of blood clots in the deep veins of the legs (deep vein thrombosis) or pulmonary embolism, physicians may prescribe low-dose anticoagulant therapy to prevent recurrent clots.

Maintaining a healthy weight and not smoking are equally important. For those confined to a bed or chair, regular movement and stretching is vital. Individuals should avoid sitting with crossed legs and wearing tight garments (e.g., garters or knee-high hosiery) below the waist. 

Whenever a patient undergoes surgery, there is the possibility of blood clot formation during the surgery or recovery period. To reduce the risk of deep vein thrombosis or a pulmonary embolism, anticoagulants may be prescribed to help prevent blood clots, especially after orthopedic procedures on the hip or knee. After surgery, cuffs that inflate intermittently may be wrapped around the patient’s legs to improve circulation and reduce the risk of blood clots. Patients scheduled for surgery should discuss their risk factors with their physician. In addition, performing calf and leg exercises before surgery and resuming activity as soon as possible after surgery can be helpful in preventing blood clots.

Finally, there is evidence that the dietary supplement ginseng may reverse the effects of the most popular anti-clotting drug. Patients who are taking anti-clotting drugs should talk to their physician about any dietary or nutritional supplements they are consuming.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to blood clots:

1. If I've been diagnosed with existing blood clots, am I at risk elsewhere in my body?
   
   
2. What steps can I take to reduce my risk of serious complications as a results of blood clots?
   
   
3. Am I at increased risk for heart attack, stroke or pulmonary embolism?
   
   
4. Should I be taking medications to reduce my risk of suffering from complications?
   
   
5. Are there any dietary supplements that I can take to reduce the risk of embolism or thromboembolism?
   
   
6. If I'm on anticoagulants, are there any dietary supplements that will help? Or hurt?
   
   
7. Will exercise or sex increase my risk of suffering from a blocked artery? Will it help?
   
   
8. Is this a permanent condition? Can it be cured?
   
   
9. Are there any surgical or minimally invasive approaches available to treat my blood clots?
   
   
10. If I lose weight, control my diet, exercise and take other steps to reduce my risk of heart attack and stroke, will this also reduce the risk of suffering complications from blood clots?