Sometimes people develop a blood clot after surgery or after sitting still for a long period of time such as on a multi-hour plane ride. The condition is called deep vein thrombosis. 

It happens when a blood clot—the medical term is "thrombus"—develops in a deep vein of the body. It occurs most commonly in the legs.

If the blood clot travels to the heart and lungs, it can cause pulmonary embolism—the sudden blocking of an artery to the lung. Combined deep vein thrombosis and pulmonary embolisms are referred to as venous thromboembolisms, which is diagnosed in about two million Americans each year, claiming more than 100,000 lives annually.

When a clot develops in a deep vein, it can block circulation. This can cause the limb to swell because blood can’t easily return to the heart. The swelling starts out mild, so it's common for people who have a DVT to not even be aware that a problem is developing.

The first symptoms may include pain, limb heaviness or a warm sensation in the area where the clot develops. With severe DVT, swelling increases and becomes more noticeable. 

The limb can become discolored, turning red or blue. These changes mean the leg or arm is starved for blood. This is a medical emergency; it can cause the loss of the limb or even death.  

People who develop deep being thrombosis often have at least two of the three following preconditions:

Slow blood flow: It can happen during long days sitting at a desk or on long plane trips or car rides. People who have had surgery or who are bedridden are also at risk for a deep vein thrombosis. The risk is higher, too, for people whose lifestyles are too sedentary overall, especially if they also have another precondition.

A hyper coagulable state: Various factors make blood more prone to clotting. The cause may be genetic, as in people with a protein C deficiency. or it may be related to medication such as contraceptives. Smoking is also a known risk factor.

An abnormality in the blood vessel: Deep being thrombosis is more common in people who have May-Thurner syndrome. This is a condition present from birth, where the iliac vein in the left leg presses against the iliac artery, which can eventually scar the vein. A blood clot can also develop in a person with thoracic outlet syndrome, which causes the vein that drains the arm to be compressed by the top rib. Finally, some vessel abnormalities are created by medical treatments, such as special catheters that are placed in the deep veins.

Although this condition is equally common in the upper and lower limbs, it is often more likely to require significant treatment if it affects a leg.

To diagnose deep vein thrombosis, your doctor will ask about symptoms like pain, swelling and a heavy feeling in the limb. “The best indicator that something is wrong is when the patient looks down and says, ‘That’s not my normal leg,’” says Todd Schlachter, MD, a board-certified interventional radiologist at Yale Medicine's Department of Radiology & Biomedical Imaging. Next the doctor will examine the limb for signs of swelling.

A blood test called D-Dimer, plus ultrasound imaging, is frequently used to help diagnose VTE. Deep vein thrombosis can be definitively diagnosed with a Doppler ultrasound procedure, an easy diagnostic exam that doesn’t involve radiation.

Lastly, your doctor will compress the vein. “Normally, the vein is very compliant. When you push on it, it will flatten out,” explains Dr. Schlachter. “But a clot is hard, so the vein will not compress.”

Treatment for DVT varies, depending on each person's particular circumstances. 

If a person develops a clot in his arm related to a catheter, perhaps one used for dialysis, chemotherapy or antibiotics, the catheter is removed. This eliminates the source of the problem. Often anticoagulant medication will be prescribed as well.

Most DVTs require only medical treatment. “The standard of care is blood thinners and compression stockings with leg elevation and sometimes a filter to catch the blood clot before it travels to the lungs,” says Dr. Schlachter.

However, if medical treatment isn't working after a few days or if the clot is already too advanced when it’s diagnosed, your doctor might try a minimally invasive procedure to remove the blood clot. This restores blood flow to the limb and prevents long term complications.

In this case, an interventional radiologist (such as Dr. Schlachter) might insert catheters into the affected vein and infuse it with a drug called tissue plasminogen activator (tPA). This is a powerful clot-busting medication. Another way to treat this is with a suction thrombectomy, which uses suction to pull the clot out of the vein. 

For protection against pulmonary embolism or other complications of DVT, especially in a person who cannot take anticoagulants, the best treatment might be to install a filter on the inferior vena cava. This is the large vein in the torso that carries blood from the lower body to the heart. The filter will catch any bits of a clot that break off during the treatment.

When a patient at Yale Medicine is diagnosed with deep vein thrombosis, specialists are called in for a multidisciplinary consultation. An interventional radiologist and hematologist work together to decide on the best treatment plan.

The hematologist draws blood and tests it to investigate the possibility of an underlying hypercoagulable state, such as a protein C deficiency. Meanwhile, the interventional radiologist determines if conservative treatment is appropriate.

“If the patient improves with conservative treatment, we may not need to do any intervention,” says Dr. Schlachter. “But we still follow-up with them in the clinic after they get discharged, to make sure they continue to improve."

Follow-up is important because even if a deep vein thrombosis is not successfully treated, it can have long-term effects. For instance, in post-thrombotic syndrome, the clot can scar the vein. This can lead to lifelong swelling and pain.

Yale Medicine patients are typically checked a week or two after discharge, then again six months late, and annually after that, depending on how the case progresses.