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Deep Vein Thrombosis

How Is It Diagnosed?

Thursday, June 14, 2012 - 13:03

Contributing Author: Guy Slowik FRCS

The diagnosis of deep vein thrombosis is suspected on the basis of signs and symptoms alone. An examination may reveal a red, swollen, tender area of the leg, particularly the calf. A sharp pain when the foot is flexed upward sometimes suggests that the individual has DVT.

Need To Know:

The importance of correct diagnosis

If a diagnosis of DVT is strongly suspected, physicians may start treatment with anticoagulant (blood-thinning) drugs before tests have confirmed the diagnosis. These drugs, however, can lead to internal bleeding. Therefore, physicians are reluctant to start treatment until tests have definitively diagnosed the condition.

For a definitive diagnosis of DVT, special imaging techniques are required.

  • Ultrasound, a diagnostic technique which uses harmless high frequency sound waves to measure blood flow in the deep veins.

    In this procedure, a detector is passed over the skin of the affected limb. Sound waves painlessly penetrate the skin, bounce back from the structures below, and are converted to electrical impulses. After processing, these impulses form an image of the tissues inside the leg on a monitor. Blood flowing through an obstructed vein creates a different image than blood flowing through a fully open vein.

  • Venography. Until recent advances in ultrasound made the procedure highly reliable, the best method for diagnosing deep vein thrombosis was venography, which is still used. It remains the "gold standard" for definitive diagnosis.

    Venography uses X-ray technology to measure blood flow in deep veins. A special harmless dye is injected into a vein in the foot. This substance then circulates throughout the veins in the leg and can be easily seen on an X-ray. If DVT is present, blockages or partial blockages in the vein are immediately seen; the dye is seen surrounding any clot that exists in the vein.

  • Blood test coagulability (clotting tendency). Various tests are used to assess the activity of the blood clotting factors. The time taken for the person's blood to clot is measured and compared with the time taken for normal blood to clot under the same conditions.
  • Other tests. Rarely, physicians will use computerized tomography scanner or CT scan (a machine that passes X-rays through the body from various angles) to diagnose DVT in the abdomen or pelvic region. In some instances, they will usemagnetic resonance imaging (MRI) . Both techniques provide high quality cross-sectional images of organs and structures within the body.
  •  If a pulmonary embolism is suspected, specialized tests will be immediately ordered. These include a lung perfusion scan or a pulmonary arteriogram, in which dye is injected into an artery and its course followed through the lungs. Any obstruction due to a clot will be seen. A perfusion scan determines if there is an area of the lung not being properly ventilated. Specialized blood tests and an EKG will also be done.

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