• Also Known As:
  • DVT
  • Blood clot in the leg
  • Thrombophlebitis
  • Venous thrombosis
  • Venous thromboembolism
  • VTE
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What is DVT?

DVT (Deep Vein Thrombosis) is the formation of a blood clot in a vein. Most DVTs originate in a deep vein in the calf or thigh, but they can also occur in other parts of the body, such as deep veins in the pelvis, abdomen or arms. These clots can restrict the flow of blood, slowing or blocking blood from returning to the lungs and heart.

Some people tend to develop clots more easily than others. DVTs can develop as a complication of excessive blood clotting disorders. You can develop an increased risk of blood clots because of pre-existing conditions, medications, or lifestyle choices, for example. Rarely, you can have a predisposition because of the genes you have inherited. (For more details, read the section on Risk Factors below.)

Left untreated, a DVT can continue to grow, eventually completely obstructing the vein and causing pain, inflammation, swelling, discoloration, and often permanent damage. Even with treatment, increased risk for another DVT can occur, as can long-term complications, called postthrombotic syndrome (PTS). This condition can lead to chronic symptoms in the affected area (e.g., leg, arm) after a DVT, such as long-term swelling, pain, aching, heaviness, tiredness, cramping, darkened skin, bluish tinge, or non-specific discomfort.

The greatest danger with DVT is not the clot in its original location, however. It is the risk of thromboembolism (obstruction of a blood vessel in a different part of the body), particularly pulmonary embolism (PE). This occurs when part of the blood clot breaks off and travels to the lungs, where it can block blood flow to the lungs. PE is a medical emergency that can be immediately life-threatening.

Together, DVT and PE are grouped into VTE (venous thromboembolism), blood clots that form in the body’s veins but not arteries. The Centers for Disease Control and Prevention (CDC) estimates that as many as 900,000 people in the U.S. could be affected by VTE each year and that 60,000 to 100,000 of those affected will die of the condition, most from PE. Sudden death is the first symptom in about 25% of those with PE.

About 30% to 50% of people with DVT will have long-term complications, and about 30% with DVT and/or PE will have another one within 10 years.


About DVT

Risk Factors

A number of conditions and factors can increase your risk of DVT. You can have more than one factor or condition that increases your risk, and the resulting risk can be cumulative. For example, if you have an inherited risk, you will likely be at greater risk if you also smoke or use oral contraceptives.

Most common risk factors are acquired later in life (you are not born with them). With some of these factors, you can make changes to lower your risk of blood clots.

Some examples of acquired risk factors include:

  • Age – the risk of clots increases the older you get (especially older than age 55).
  • Chronic conditions such as cancer (recent or recurrent), heart disease (e.g., congestive heart failure), kidney disease (e.g., nephrotic syndrome), lung disease
  • Catheter placed in a central vein – this is a tube that is placed into a main vein of the body so that fluids and medications can be administered. These are especially associated with DVTs that occur in the upper body.
  • Increase in the hormone estrogen – from medications (estrogen-based birth control or hormone replacement therapy) or from pregnancy (during and for up to 3 months after delivery of the baby)
  • Personal history of DVT – once you have had a blood clot, you are at increased risk of having another one.
  • Immobility – prolonged bed rest or sitting for long periods of time slows blood flow and calf muscles are not contracting to help circulate the blood; anything that slows blood flow for a significant amount of time, sometimes even for a few hours, such as might happen during a long plane ride. This is called venous stasis or more commonly “coach class syndrome”.
  • Surgery, especially surgery involving the abdomen or pelvis and orthopedic surgeries, such as knee or hip surgeries; there can be an activation of tissue factors that increase the risk of clotting as well as increased immobility during recovery.
  • Hospital stay – 50% of blood clots occur during or soon after a hospital stay or surgery.
  • Inflammatory bowel disease
  • Antiphospholipid syndrome (APS) – an excessive clotting disorder
  • Injury to a vein – injury to the walls of veins from fractures, muscle injuries or other trauma can promote formation of blood clots.
  • Obesity
  • Smoking

Rarely, people inherit genetic variations (mutations) that increase the risk of inappropriate clotting. Some of the most common inherited risk factors include:

Signs and Symptoms

About half of people with DVT have no or few noticeable signs and symptoms. If you do have symptoms, they may develop suddenly or gradually and may include:

  • Buildup of fluid, swelling (edema) in the affected leg
  • Pain or tenderness in the leg (clots that develop rapidly often cause more pain than those that develop slowly)
  • Redness and/or warmth of the skin in the leg

If a piece of the clot breaks off and travels to the lungs, you have a pulmonary embolism (PE). Signs and symptoms of PE may develop quickly and include:

  • Chest pain that worsens with deep breathing or coughing
  • Coughing up blood
  • Difficulty breathing
  • Fast or irregular heartbeat
  • Very low blood pressure, fainting


Laboratory Tests

Before you have testing done, you will first be evaluated to estimate your probability of having a DVT. The evaluation takes into account several factors, such as your medical history and signs and symptoms.

  • Based on the evaluation, if your pre-test probability is low to medium, then you will likely have a D-dimer test first. A negative D-dimer result rules out a DVT. A positive result may be caused by a DVT or many other conditions, so one or more imaging tests (see below) are required for diagnosis.
  • If your pre-test probability is high for a DVT, then a D-dimer test is often not done. Instead, you will have one or more imaging tests (see below).

The above recommended steps are from the American Society of Hematology (ASH), the American Academy of Family Physicians (AAFP), and American College of Physicians (ACP).

Some general laboratory tests may be done at the same time as an initial evaluation:

Tests to help diagnose the underlying cause:

If you are diagnosed with a DVT and you don’t have classic risk factors, or you have a DVT at a young age (younger than age 50) or in an unusual location, additional tests may be done to determine the underlying cause. This testing is important to help determine your risk of having recurrent DVTs.

Some tests may be done while you are treated for a DVT. Examples include:

Some tests are affected by an existing blood clot or by treatment for a DVT and cannot be done until after your clot has been treated and resolves. Your healthcare practitioner may then order the following tests several weeks or months later to help determine the cause of your DVT. These tests help detect deficiency in blood clotting factors:

Tests to monitor treatment:

  • PT/INR (international normalized ratio)—to monitor warfarin therapy
  • PTT—to monitor standard (unfractionated) heparin therapy
  • Heparin anti-Xa—to monitor standard heparin therapy and sometimes to monitor low molecular weight heparin (LMWH) therapy
  • Warfarin sensitivity testing—test may be ordered if warfarin therapy is prescribed; this test helps determine your likely sensitivity or, less commonly, resistance to warfarin and helps your healthcare practitioner select appropriate doses.

If you are receiving heparin therapy and your platelet count significantly decreases (thrombocytopenia), especially if you also have new blood clots, you may have a test for heparin-induced thrombocytopenia antibody (PF4 antibody). The test detects antibodies that develop in some people treated with heparin. If indicated, the test helps diagnose immune-mediated heparin-induced thrombocytopenia (HIT type II), a condition that causes a low platelet count (thrombocytopenia) and excessive clotting (thrombosis).

Non-Laboratory Tests

An imaging test or series of imaging tests may be done to help locate a clot that has formed in a vein. Some examples include:

  • Ultrasound (most commonly used)
  • Venography
  • Impedance plethysmography

Some imaging tests may be done to locate a suspected pulmonary embolism (PE). Examples include:

  • MRI
  • CT angiography
  • Pulmonary V/Q scan

For more information on these imaging tests, see RadiologyInfo.org.


Prevention of first-time DVT and PE and recurrent DVTs starts by minimizing the risk factors that you can, such as:

  • Avoiding sitting still for extended periods of time by walking around every 2 to 3 hours
  • Moving as soon as you are allowed to after being confined to bed
  • Moving as soon as you are permitted after a surgery and/or using mechanical means of helping to move the blood in the legs (such as pneumatic sleeves that fit over the legs and pulse pressure)
  • Receiving medications prior to, during, and following a surgery to help prevent a DVT
  • Quitting smoking
  • Being aware of the risk factors and communicating with your healthcare practitioner about them
  • Taking prescribed anticoagulant (“blood thinning”) therapy, short or long-term, that is individually tailored to your situation. (See Treatment below for details.)

Prevention of PTS and Symptom Relief

Graduated compression socks may be prescribed to help prevent postthrombotic syndrome (PTS) and leg swelling as well as to help with symptom relief. They are elastic stockings that are fitted to each person and are very tight at the ankle and then less tight up the calf.


The medications available to treat DVT are constantly evolving:

  • Anticoagulants – these are the most common treatments for DVT. They stop a blood clot from growing bigger while the body slowly reabsorbs it. They also help prevent new ones from forming. There are a number of these medications that can be given by injection or taken as pills. Each of these carry a risk of causing bleeding episodes. Some require monitoring with blood tests, some do not. The risks, benefits and costs of various anticoagulants should be discussed with your healthcare practitioner.
  • IVC filter placement – if indicated based on clinical assessment, a filtering device can be placed within the inferior vena cava (IVC, a large vein in the abdomen that returns blood from the lower part of the body to the heart) to prevent clots from going to the lungs.
  • Thrombolytic/Thrombolysis (commonly called “clot busters”) – in severe cases, medications can be injected into the blood or directly delivered through a catheter to the site of the clot in the vein. They dissolve the clot but carry a risk of causing serious bleeding (such as inside the head).
  • Surgical clot removal – this procedure may be done through a variety of methods, including with the use of directed catheter and balloon. Surgical removal of a clot may be performed when you cannot be given anticoagulants, but it carries its own risks.

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