How Are Blood Clots Diagnosed?

If you’re experiencing symptoms that could indicate a blood clot, then it’s important to seek medical care as soon as possible. Once you do that, what happens next? What’s the process of diagnosis of a blood clot?

The first step in the process is for your medical team to see you and learn about your symptoms. Be prepared to answer questions about when your symptoms started, how they’ve been progressing since then, and exactly what they feel like. You’ll also get a physical exam, and they’ll look for signs of a clot. This generally includes comparing one side of the body to the other.

If you have any potential risk factors for a clot, make sure that you mention those to your medical team. These are factors that make you more likely to experience a clot, such as recent long-distance travel. It’s likely that they’ll ask, but in case they don’t, it’s a good idea to mention these factors. The more risk factors you have, the more likely it is that your symptoms are due to a clot. (Although it’s important to keep in mind that even a person with no risk factors at all can still experience a clot.)

After this, your medical team will perform a series of tests. This will determine whether you have a clot, and if so, where it’s located. The most commonly used tests are:

  • Blood tests: A small protein fragment called D-dimer is produced when blood clots are breaking down. People with a DVT or PE will generally have elevated levels of D-dimer.
  • Ultrasound: This uses sound waves to look at the veins, to see how blood is flowing through them. This test is generally considered to be the standard for diagnosing DVT.
  • Chest X-ray: A chest X-ray may be performed first, to rule out other possible causes of your symptoms. However, the X-ray actually won’t show a PE. It’s used to verify that you don’t have another condition that could cause similar symptoms, such as pneumonia.
  • Chest CT: This test is used for diagnosing PE. In a CT, a machine uses X-ray images to generate a 3D model of the inside of your body. Contrast dye may be injected through a vein, to make it easier to see your blood vessels on the CT.
  • V/Q scan: Also known as a ventilation/perfusion scan, this test compares the air flow and blood flow within your lungs. Through a mask, you breathe air that’s been labeled with a tracer. Contrast dye is also injected into your veins. If there’s an area of normal air flow but reduced blood flow, a PE is likely the cause.

In some cases, other types of tests may be used, such as:

  • Venography: This test uses X-rays to look at the veins of the legs, to check for clots. A dye is injected into a vein, and then a series of X-rays is taken. Because ultrasound is less invasive and doesn’t involve radiation, it’s much more commonly used, and venography is only used rarely.
  • MRI: This type of imaging uses strong magnets to create images of the inside of the body. MRIs are sometimes used to look for clots in internal parts of the body, such as the abdomen. They can also be used in patients for whom exposure to radiation is a concern.
  • Pulmonary angiogram: This test can be used to diagnose PE. For this test, a long flexible tube called a catheter is inserted through a vein in your leg, and threaded up through blood vessels until it reaches your pulmonary arteries. Then contrast dye is injected through the catheter, and X-rays are taken to look at your pulmonary arteries. Because this is an invasive test, it’s generally only used when other types of testing have failed to provide a diagnosis.

The specific tests that are needed in your situation depend on many factors. Your medical team will talk with you about what tests they’re ordering and why. Feel free to ask questions; it’s your right to fully understand the plan for your medical care.

Prompt treatment of a blood clot can reduce the risk of damaging or even life-threatening consequences. That’s why it’s important to get a proper diagnosis. If your team finds that you have a blood clot, then they can move on to creating the best treatment plan for you.

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