Deep Vein Thrombosis (DVT) occurs when a blood clot (thrombus) forms in one or more of the deep veins in the body, mainly in the lower leg and thigh, but can occur in other deep veins such as in the arms and pelvis. It can cause leg pain or swelling, but may occur without any symptoms.

DVT is a serious condition because blood clots in the veins can break loose, travel through the bloodstream and lodge in the lungs, blocking blood flow (pulmonary embolism). This can be prevented by prescribed medications, like blood thinners that also help reducing chances of recurrent blood clot.

This condition can be prevented by maintaining a good activity level that keeps blood moving around the body without pooling in the deep veins. Persons with high risk may require wearing graduated compression stocking. Visiting doctor regularly for those people is also important.

DVT is the presence of coagulated blood called thrombus in one of the deep venous conduits that return blood to the heart, most commonly involves the deep veins of the legs or arms. This condition often resulting in potentially life-threatening emboli to the lungs or chronic leg disturbance.

Blood clots can form in the body's deep veins if:

• A vein's inner lining is damaged. Injuries caused by physical, chemical, or biological factors can damage the veins. Such factors include surgery, serious injuries, inflammation, and immune responses.
• Blood flow is sluggish or slow (Venous stasis). Lack of motion can decrease blood flow. This may occur after surgery, if the person ill and in bed for prolong period, or with traveling for a long time.
• Blood is thicker or more likely to clot than normal. Some inherited conditions (such as factor V Leiden) increase the risk of blood clotting. Hormone therapy or birth control pills also can increase the risk of clotting.

• A history of Deep Vein Thrombosis.
• Some inherited blood disorders, such as factor V Leiden.
• Hormone therapy with Estrogen or birth control pills.
• Injury to a deep vein from surgery, a broken bone, or other trauma.
• Lack of movement like after surgery, bed ridden persons and long-time traveling.
• Pregnancy and the first 6 weeks after giving birth.
• Recent or ongoing treatment for cancer.
• A central venous catheter (a tube placed in a vein to allow easy access to the bloodstream).
• Older age, mainly after 60 years, although DVT can occur at any age.
• Overweight or obesity.
• Smoking.

Thrombosis is the homeostatic mechanism whereby blood coagulates or clots, a process crucial to the establishment of hemostasis after a wound. It may be initiated via several pathways, usually consisting of cascading activation of enzymes that magnify the effect of an initial trigger event.

Venous stasis can occur as a result of anything that slows or obstructs the flow of venous blood. This results in an increase in viscosity and the formation of microthrombi, which are not washed away by fluid movement; the thrombus that forms may then grow and propagate. Endothelial damage in the blood vessel may be intrinsic or secondary to external trauma.

An increased coagulability state can occur due to a biochemical imbalance between circulating factors. This may result from an increase in circulating tissue activation factor than enhance aggregation to form clot, combined with a decrease in circulating plasma antithrombin and fibrinolysins which act against the net that trap blood cells and platelets to make a thrombus.

Only about half of the people who have DVT have signs and symptoms. The manifestations occur in the affected leg include:

• Swelling of the leg or along a vein in it.
• Tenderness in the leg, which may be felt only when standing and walking.
• Pain in calf when flexing the foot (Homan’s sign), or when pressing on the calf (Meyer’s sign), or pain is the sole when pressing on the medial part of the leg (Pyar’s sign).
• Increased warmth in the area of the leg that's swollen or painful.
• Red or discolored skin on the leg.

If the person developed pulmonary embolism signs of this condition may appear. These include shortness of breath and Pain with deep breathing or coughing.

When the health care provider thinks about DVT based on the symptoms, some tests may be done to make confirmation. These include:

• D-dimer test: a blood test used to check for blood clotting problems. The normal result is negative, if not, this means that making blood clots is in progress. The test does not tell where the clots are or why it is made. Your provider may order other tests to see where clots are located.
• Ultrasound. A transducer placed over the part of the body where there's a clot sends sound waves that travel through the tissue and reflect back, a computer transforms the waves into a moving image on a video screen. A clot may be visible in the image. Sometimes a series of ultrasounds are done over several days to determine whether a blood clot is growing or to be sure a new one hasn't developed.
• Venography. A contrast medium is injected into a large vein in the foot or ankle. An X-ray procedure creates an image of the veins in your legs and feet, to look for clots. However, less invasive methods of diagnosis, such as ultrasound, can usually confirm the diagnosis.

• Blood thinners (anticoagulants). Medications that decrease the blood's ability to clot can prevent thrombus from getting bigger or reduce the risk of developing additional ones. Person first is given a shot or infusion of the blood thinner heparin for a few days. Then treatment may be followed by another injectable blood thinner, such as enoxaparin, dalteparin, or fondaparinux. Other blood thinners can be given in pill form, such as warfarin and rivaroxaban. It’s important to take medications exactly as instructed by the doctor. Blood-thinning medications can have serious side effects like bleeding. Periodic blood tests to check how effective and safe is the treatment with these drugs are also recommended.
• Thrombolytics. Also called tissue plasminogen activators (TPA), these drugs are given to break up blood clots. It can cause serious bleeding and are generally used only in life-threatening situations. For these reasons, thrombolytic medications are only given in an intensive care unit. It is only given with more serious type of deep vein thrombosis or pulmonary embolism, or if other medications aren't working.
• Graduated compression stockings. This kind of wear helps prevent swelling associated with deep vein thrombosis. Stockings are worn on the legs from the feet to about the level of the knees. This pressure helps reduce the chances that blood will pool and clot. Patients are advised to wear these stockings during the day for at least two to three years if possible.
• Surgical procedures. Surgery may be needed if medications do not work or if the condition was large. Surgical treatment may involve: removing a large blood clot from the vein or injecting clot-busting medications, widening the vein lumen through balloon catheterization, and placing a filter in the body's largest vein (inferior vena cava) to prevent blood clots from traveling to the lungs.

The two main complications of deep vein thrombosis are pulmonary embolism and post-thrombotic syndrome.

• Pulmonary embolism

It is the most serious complication of DVT. It happens when a piece of blood clot breaks off and travels through the bloodstream to the lungs, where it blocks one of the blood vessels. In severe cases this can be fatal. If the clot is small, it might not cause any symptoms. If it's medium-sized, it can cause chest pain and breathing difficulties. A large clot can cause the lungs to collapse, resulting in heart failure, which can be fatal. About 10% of people with an untreated DVT develops a severe pulmonary embolism.

• Post-thrombotic (postphlebitic) syndrome

Having DVT may lead to developing long-term symptoms in the calf known as post-thrombotic syndrome. This affects around 20-40% of people with a history of DVT. The blood clot in the vein of your the can divert the flow of blood to other veins, causing an increase in pressure. This can affect the tissues of your calf and lead to symptoms, including: calf pain, swelling, a rash, and ulcers on the calf. Being obese or over weight will increase the risk of this condition.

Many steps are considered trusting to prevent deep vein thrombosis (DVT) and pulmonary embolism (PE). If the person is at risk for these conditions, he/she is advised to:

• See the doctor for regular checkups.
• Take all medications as prescribed.
• Get out of bed and move around as soon as possible after surgery or illness.
• Exercise the lower leg muscles during long trips.
• Lose excess kilograms and maintain a healthy weight.

For persons who had DVT or PE before, they can help prevent future blood clots through Follow the steps above and:

• Take all medicines that prescribed to prevent or treat blood clots
• Use graduated compression stockings as directed by the doctor.
• Get rid of smoking or alcohol drinking.

DVT often goes away without a problem, but there is a chance for some cases to deteriorate, especially with large thrombosis or that lead to pulmonary embolism the responsible for the majority of DVT deaths by 3% of them.

The outcomes depend on the medical history. Those who have it before are at greater risk to develop this condition again.  It is recommended here to strict adherence to protective measures. One of the crucial things in DVT is how fast is the speed of treatment care, as thrombus cannot be removed by its medications except for short period after the clot has formed.

Deep vein thrombosis (DVT) and pulmonary embolism (PE) are manifestations of a single disease entity, namely, venous thromboembolism (VTE). A systematic review for the global burden of the VTE took place under the supervision of researchers from many health institutes like patient safety program, WHO had found that around 10 million cases around the world are diagnosed every year. VTE-related events in United States and Europe kill more people than AIDS, breast cancer, prostate cancer and motor vehicle crashes combined.