Compression Ultrasound

leg pain
Leg pain. Imagesbybarbara/Getty Images

Compression ultrasound is a non-invasive test used to diagnose deep venous thrombosis (DVT), a condition in which a blood clot has formed in the deep veins of the leg. Compression ultrasound has some advantages over other diagnostic tests for DVT — it can be readily performed in most institutions, it gives accurate results, and there is very little risk associated with it.

Importance of DVT

Thrombosis of a leg vein causes obstruction of the vein, preventing blood from returning easily to the heart.

As a result, DVT often produces pooling of blood in the leg, producing pain, redness and swelling. These symptoms can become chronic if the DVT is not treated adequately.

Even more importantly, a blood clot in a leg vein can break loose and travel to the lungs, thus causing a pulmonary embolus. A pulmonary embolus — which is estimated to occur in between 10% and 50% of people who have DVT — is a very serious condition that can produce severe dyspnea (shortness of breath), cardiac instability, and death.

For this reason, if DVT is suspected it is important to make a definitive diagnosis as quickly as possible. Early treatment with anticoagulant drugs is critically important in preventing a pulmonary embolus, or (if one has already occurred) in preventing another pulmonary embolus.

Compression Ultrasound

In the past, making a firm diagnosis of DVT required performing a venogram. With a venogram, dye is injected into a leg vein, and x-ray images are made of the dye flowing through the veins back toward the heart.

Major obstructions to the leg vein can be visualized. This invasive test can be painful, time consuming, and entails certain risks, such as the risk of infection.

In some institutions, a noninvasive test called impedance plethysmography is used to diagnose DVT. While this test is reliable, many hospitals do not have the equipment or the expertise readily available to perform this test efficiently.

In recent years, the compression ultrasound technique has been validated as a quick, safe, painless, reliable and noninvasive method for diagnosing DVT. In most institutions it has supplanted venograms and impedance plethysmography as the diagnostic test of choice for DVT.

Compression ultrasound is a variation of the commonly used medical ultrasound technique (also known as an “echo” test). in which sound waves are applied to tissue by means of a probe placed on the skin, and an image of the tissue beneath the probe is constructed from the returning sound waves. Because the equipment for compression ultrasound is readily available in all modern hospitals, and because the technique for performing it is relatively easy to learn, compression ultrasound has become the go-to method in most institutions for diagnosing DVT.

To perform compression ultrasound, the ultrasound probe is placed over the suspect vein to produce an ultrasound image of the vein. The operator then attempts to compress the vein by pushing on it with the ultrasound probe.

Veins are typically highly compressible; that is, veins can be collapsed temporarily by applying pressure to them. And it is easy to visualize the compression of a vein with ultrasound.

But if DVT is present, the presence of a blood clot makes it much more difficult to compress the vein. When the vein is non-compressible, that is a reliable indicator that DVT is present. The ultrasound technique can also be used to attempt to visualize the clot itself, and to assess the flow of blood through the vein to see whether an obstruction is evident. However, the non-compressibility of the vein is the most helpful aspect of the study in detecting a DVT.

In a typical study to look for DVT, vein compressibility is tested in two particular spots — the femoral vein (in the groin area) and the popliteal vein (behind the knee).

Studies have shown that, using this 2-point compression technique, DVT can be accurately diagnosed over 90% of the time.

Because it can be performed readily in almost any hospital setting, because it gives accurate results, and because there are virtually no side effects, compression ultrasound has become the diagnostic test of choice in most institutions for diagnosing DVT.


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