DVT Tests and Diagnosis

If you think you may have deep vein thrombosis (DVT), the best thing you can do is call your doctor as soon as possible. There are several ways that they can figure out if you have this potentially dangerous type of blood clot.

Tests for DVT

At your appointment, you and your doctor will discuss your symptoms and your medical history. You'll also get a physical exam. Your doctor will use all of that to determine if you might be at risk for DVT. If they think you might have it, your doctor can confirm it with one or more of these tests.

D-dimer test. This blood test checks for a protein called D-dimer. It's what a blood clot makes as it dissolves inside your body.

If the results show low or normal levels of this protein and your doctor believes you're at low risk for a clot, you probably don’t have DVT. But if you have high levels of D-dimer, you might have a blood clot. Your doctor can find out with other tests, while also ruling out other conditions that can bring on high D-dimer, like pregnancy and heart disease.

You can get the D-dimer test in your doctor's office. For other tests, you may need to go a hospital or radiology clinic. For example:

Ultrasound. This is often the main imaging test for diagnosing DVT. It uses sound waves to make pictures of the inside of your body. The pictures can show the blood in your veins and any clots.

The technician who does your test captures these images by moving a wand-like device over your skin on the part of your body that might have DVT. You’ll lie on your back and then on your stomach while they do this. They may also gently press on your veins to see if they’re stiff, which could signal a blood clot.

If you’re at a high risk for DVT, then you doctor might not do the D-dimer test and right away order an ultrasound of your leg or calf.

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MRI. For this imaging test, you’ll lie inside a tube-shaped machine that scans your body with a magnetic field and radio waves. It’s painless, and you can ask for medicine to help you feel calmer if an enclosed space makes you anxious. The technician who does the test watches you from another room, and you should be able to talk with them over a microphone in the machine if you need to. Doctors don’t use MRI as commonly as ultrasound to diagnose DVT.

Contrast venography. This imaging test uses special dye and an X-ray to spot a blood clot in a deep vein. Doctors rarely diagnose DVT with it anymore, though. Before the test, you lie down on an X-ray table, and a member of your care team places a needle called an IV into a vein in your foot or ankle. Then they inject dye, which allows the deep veins in your leg or hip to stand out in X-ray images.

Tests Related to DVT

DVT can bring on a dangerous condition called a pulmonary embolism (PE). For some people, a PE is the first sign they have DVT.

A pulmonary embolism is when a deep-vein clot breaks loose, travels to your lungs, and gets stuck in an artery there. It blocks normal blood flow. It’s an emergency that can be deadly.

You could have symptoms like:

Your doctor may give you the D-dimer blood test to figure out how likely it is that you have a pulmonary embolism. If your result is normal and your other risks are low, you probably don’t have a PE. If the doctor says your result isn’t normal, they’ll recommend one or more of these other tests. You’ll need to go to a hospital or radiology clinic to get them.

Computed tomography (CT) pulmonary angiogram. This is the most common imaging test for diagnosing PE. It uses a special X-ray to scan your lungs for a blockage from a blood clot. It can also spot DVT in your legs.

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Before the test, your care team will give you dye through an IV. It goes into your arteries and makes signs of PE visible in the images that your technician will capture. You’ll lie on a table that slowly moves through a doughnut-shaped machine called a CT scan, a device that takes X-ray pictures of your lungs from different angles.

Pulmonary angiogram. This less common type of X-ray test also uses dye to spot a PE. Before the test, your care team gives you a sedative to help you relax. Then they put numbing medicine on your arm or groin and insert a thin, hollow tube called a catheter into a vein. You may feel a bit of pressure as they guide the catheter through your heart’s right side and into your pulmonary artery. This lets them see movie-like images of your lungs. After they’ve placed the catheter there, they'll inject dye through it, which will help them see if a DVT clot is blocking blood flow.

Ventilation-perfusion scan. If you can’t get a CT pulmonary angiogram, your doctor may recommend this imaging test. They may call it a VQ scan. The test scans your lungs in two ways to create pictures of the oxygen and blood flowing through them. If a part of either lung is getting the right amount of oxygen but not enough blood, it could be a sign that a DVT clot is causing a pulmonary embolism.

During the test, you’ll lie on a table while a scanner takes pictures from different angles. Half of the test involves taking pictures of the airflow in your lungs. Your technician may call this the ventilation scan. Right before it, you’ll breathe a mixture of oxygen and radioactive gas through a mask you wear over your nose and mouth.

You don’t need to wear it for the other half of the test, which takes pictures of your blood flow. This is called the perfusion scan. Before it, a technician gives you radioactive dye through an IV. This allows your blood flow to show up in the images.

If the idea of radioactive dye sounds a bit scary, just know that’s it’s a small amount, and it shouldn’t give you side effects.

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Do I Need to See a Specialist?

If your doctor diagnoses you with DVT, treatments like medication and compression stockings may be enough to get rid of your blood clot and prevent another one from forming. But there’s a chance you’ll need other treatments or follow-up care from a doctor who has extra medical training in blood or blood vessel diseases.

Your doctor might refer you to a blood specialist called a hematologist if you keep getting DVT or if you have a blood clotting disorder. They could send you to a vascular surgeon if they think you need surgery to get rid a blood clot.

WebMD Medical Reference Reviewed by Brunilda Nazario, MD on January 27, 2021

Sources

SOURCES:

UpToDate: “Patient education: Deep vein thrombosis (DVT) (Beyond the Basics),” “Patient education: Pulmonary embolism (Beyond the Basics).”

CDC: “Venous Thromboembolism (Blood Clots): Diagnosis and Treatment,” “Venous Thromboembolism (Blood Clots): What Is VTE?”

National Heart, Lung, and Blood Institute: “Venous Thromboembolism,” “Lung VQ Scan.”

Society for Vascular Surgery: “Pulmonary Embolism.”

American Lung Association: “Learn About Pulmonary Embolism.”

Medline Plus: “D-Dimer Test.”

UCSF Health: “Pulmonary Angiography.”

Harvard Medical School: “Ventilation-Perfusion Scan or V-Q Scan.”

Johns Hopkins: “Hematology.”

Cleveland Clinic: “Deep Vein Thrombosis (DVT): Diagnosis and Tests,” “Deep Vein Thrombosis (DVT): Management and Treatment.”

Mayo Clinic: “Deep vein thrombosis (DVT),” “MRI,” “CT Scan.”

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