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Diagnosing Deep Vein Thrombosis

NYU Langone doctors are experts at recognizing and working quickly to resolve deep vein thrombosis, or DVT, a blood clot that usually forms in a leg. Occasionally, these clots develop in the veins of the pelvis or an arm.

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Veins return blood to the heart, as opposed to the arteries, which send blood from the heart to the rest of the body. When a deep vein thrombosis creates a blockage, the blood can’t return to the heart from the leg. This can lead to sudden swelling and pain in the leg.

If not treated quickly, a clot or clots can break loose and travel through the bloodstream to one or both lungs. The clot can reduce or even stop the flow of oxygenated blood from the lungs to the heart and the rest of the body. This related and potentially life-threatening complication is called a pulmonary embolism. While the exact numbers are unknown, deep vein thrombosis and pulmonary embolism affect as many as 900,000 Americans a year.

Risk Factors

Certain factors increase a person’s risk of developing deep vein thrombosis. One of the main causes is prolonged immobility. Remaining in the same position for long periods of time makes blood pool in the legs and allows clots to form. This can happen in people who are confined to bed while recovering from surgery or those who sit in the same position for hours on an overseas flight.

People at increased risk include those who have a family history of deep vein thrombosis or inherited disorders known as hypercoagulable states or thrombophilia, which make the blood more likely to clot. At NYU Langone’s Cardiovascular Thrombosis Program, our team of specialists provides complete evaluation, diagnosis, prevention strategies, and ongoing care for people with clotting conditions, including blood clots.

Many types of cancer—including lung cancer, ovarian cancer, and pancreatic cancer—increase a person’s chance of developing deep vein thrombosis. Chemotherapy can also increase the risk. It’s not clear why, but it may be because chemotherapy can damage blood vessels and reduce the production of proteins that keep blood from clotting.

Pregnancy raises a woman’s risk of deep vein thrombosis. The weight of an unborn child puts additional pressure on the pelvis and the veins in the legs, which can affect blood flow. Hormonal changes that occur during pregnancy can also increase risk. If you are pregnant and concerned about your risk, speak with your obstetrician.

Signs and Symptoms

Two main symptoms are associated with deep vein thrombosis: swelling in the affected leg and cramping or soreness. Having symptoms in both legs is rare. When that happens, it usually suggests a more central clot in the inferior vena cava, the large vein that carries blood from the lower body to the heart.

If you experience swelling and pain in one of your legs, NYU Langone doctors assess your symptoms with a series of diagnostic tests to determine whether you have deep vein thrombosis.

You should seek medical attention immediately if swelling and pain in your leg is followed by a sudden appearance of additional symptoms such as shortness of breath, lightheadedness, fainting, chest pain, rapid heartbeat, and coughing up blood. These can signal pulmonary embolism, a medical emergency.

Diagnostic Tests

In addition to performing a physical examination and asking about your medical history, your doctor may order tests to look for signs of deep vein thrombosis.

Blood Test

When a blood clot breaks up in the body, it releases a substance called D-dimer. Many people who have deep vein thrombosis also have an elevated level of D-dimer in the blood. Although the results of this blood test can’t confirm a diagnosis, a negative result can help rule out deep vein thrombosis. Doctors can also use the test later to assess how treatments are working, as well as determine the risk of a future blood clot.

Venous Duplex Ultrasound

This test combines conventional ultrasound with Doppler ultrasound, which uses sound waves to show the flow of blood through blood vessels. Doctors may use this test to examine the legs and determine whether there is a narrowing or blood clot that may indicate deep vein thrombosis.

Venous duplex ultrasound takes about 30 to 60 minutes and does not cause discomfort.

CT Scans

In a CT scan, X-ray technology is used to take multiple three-dimensional pictures of the inside of the body. At NYU Langone, our doctors regularly use CT scans with the least amount of radiation possible to obtain images of veins, which can reveal blood clots.

Just before the scan begins, you may be given an intravenous (IV) dose of a solution that contains a contrast material, or dye. This liquid travels through the veins and makes blood clots more visible.

The test typically takes 10 to 15 minutes. It does not hurt, but you may feel a warm sensation throughout your body from the IV contrast material.

MRI Scans

In an MRI scan, a magnetic field and radio waves are used to create computerized, two- or three-dimensional pictures of structures in your body. Doctors may use this test in people who should not have a CT scan, such as those who have renal insufficiency—poorly functioning kidneys—or an allergy to iodine, a substance used in CT contrast dyes.

Before the test, your doctor may inject a contrast dye that’s not iodine based into your vein, which allows blood vessels and arteries to be seen clearly on the MRI scan. It doesn’t hurt, but you may feel a warm sensation throughout your body.

A technician takes the pictures while you lie very still on a sliding table that fits into a cylinder. The test takes 40 to 90 minutes.


During a venogram, doctors use a needle stick to place an IV line in the groin or arm. Then they insert a thin, flexible tube called a catheter through the IV into a vein and thread the catheter to the area where a blood clot is suspected. A contrast dye, slowly injected into the catheter, helps illuminate the movement of blood through the vessel. This movement is captured on X-ray images in a technique called fluoroscopy.

This test is used if the doctor also plans to treat blood clots directly with thrombolytic, or clot-busting, medication or removal of the clot by thrombectomy.

After the test, the catheter is removed. A venogram takes about 30 minutes.

Our Research and Education in Deep Vein Thrombosis

Learn more about our research and professional education opportunities.