Thrombosis and Embolism Chapter 7

Tests & Diagnosis for DVT

Diagnosis of DVT

To determine whether a DVT is present, the doctor will ask the patient about his or her health, medical history, and symptoms. However, a DVT may be asymptomatic (without symptoms), or pain and swelling may be very slight. Moreover, symptoms of DVT are common to other conditions as well. Special tests may be needed to confirm the presence of a DVT, including:

  • Ultrasound exam.Ultrasound exam is the most commonly used test for DVT. High-frequency sound waves travel through the body tissue, echo back, and are translated into moving images on a video screen. Ultrasound exams are painless, inexpensive, and readily available. Two forms of ultrasound may be used to diagnose DVT:
    • Duplex ultrasound combines two types of ultrasound, allowing the doctor both to measure the speed of blood flow and to see the structure of the veins and any clots that may be present.
    • Compression ultrasound combines ultrasound images with compression. Gentle pressure is applied to the vein with an ultrasound probe. If the vein can be compressed, this indicates there is no blood clot. If the vein resists compression, the presence of a blood clot is likely.
  • Blood test. Blood tests are given to detect the presence of D-dimer, a protein produced by clot degradation, which occurs when plasmin dissolves the fibrin strands that hold the blood clot together. Almost everyone with a DVT has an elevated level of D-dimer. However, levels of D-dimer are elevated in other conditions as well. As a result, D-dimer testing is most useful for ruling out DVT, rather than confirming its presence.
  • Venography. In a venography, radioactive dye is injected into a large vein in the foot or ankle to highlight the veins of the feet and legs. An X-ray of the area is then taken to reveal the presence of a clot. Venography is considered the gold standard for diagnosing DVT. However, venography is invasive, painful, and expensive, and so is generally used only when the doctor suspects the presence of DVT but an ultrasound exam doesn't confirm the diagnosis.
  • Computerized tomography (CT) scan. CT scans use special X-ray equipment to obtain cross-sectional pictures of the body. A contrast dye may be administered intravenously to enhance images of the blood vessels. The patient lies still on a large table that slowly passes through center of a large X-ray machine, and images of the inside of the body are displayed on a computer screen.
  • Magnetic resonance imaging (MRI). MRIs use radiofrequency waves and a strong magnetic field to create detailed images of body's interior. A contrast dye may be introduced intravenously. The patient lies still on a table that enters into the center of a large cylindrical magnet. MRIs can provide information that wouldn't appear on an X-ray, and they are effective in locating DVT in the pelvis, as well as in the leg. However, MRIs are much more expensive than other tests for DVT.

More on this topic

What Are Thrombosis & Embolism? (VIDEO)

Your Blood Moves

Thrombus & Embolus

Symptoms & Risk Factors

Blood Must Flow

Consequences of Clots

Tests & Diagnosis for DVT

Prevention & Treatment

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