Tests and diagnosis

By Mayo Clinic Staff

To diagnose deep vein thrombosis, your doctor will ask you a series of questions about your symptoms. You'll also have a physical exam so that your doctor can check for any areas of swelling, tenderness or discoloration on your skin. Depending on how likely you are to have a blood clot, your doctor may suggest further testing, including:

  • Ultrasound. A wand-like device (transducer) placed over the part of your body where there's a clot sends sound waves into the area. As the sound waves travel through your tissue and reflect back, a computer transforms the waves into a moving image on a video screen. A clot may be visible in the image.

    Sometimes a series of ultrasounds are done over several days to determine whether a blood clot is growing or to be sure a new one hasn't developed.

  • Blood test. Almost all people who develop severe deep vein thrombosis have an elevated blood level of a clot-dissolving substance called D dimer.
  • Venography. A dye (contrast agent) is injected into a large vein in your foot or ankle. An X-ray procedure creates an image of the veins in your legs and feet, to look for clots. However, less invasive methods of diagnosis, such as ultrasound, can usually confirm the diagnosis.
  • CT or MRI scans. Both computerized tomography (CT) scan and magnetic resonance imaging (MRI) can provide visual images of your veins and may show if you have a clot. Sometimes a clot is found when these scans are performed for other reasons.
Jul. 03, 2014

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