A duplex ultrasound is a test to see how blood moves through your arteries and veins.

The test combines traditional ultrasound with Doppler ultrasonography. Regular ultrasound uses sound waves that bounce off blood vessels to create pictures. Doppler ultrasound records sound waves reflecting off moving objects, such as blood, to measure their speed and other aspects of how they flow.

There are different types of duplex ultrasound exams. Some include:

• Arterial and venous duplex ultrasound of the abdomen examines blood vessels and blood flow in the abdominal area.
• Carotid duplex ultrasound looks at the carotid artery in the neck.
• Duplex ultrasound of the extremities looks at the arms or legs.
• Renal duplex ultrasound examines the kidneys and their blood vessels.

The test is done in the ultrasound or radiology department.

You may need to wear a medical gown. You will lie down on a table, and the ultrasound technician will spread a gel over the area being tested. The gel helps the sound waves get into your tissues.

A wand, called a transducer, is moved over the area being tested. This wand sends out the sound waves.

You need to stay still during the exam. You may be asked to lie in different body positions, or to take a deep breath and hold it.

A computer measures how the sound waves reflect back, and changes the sound waves into pictures. The Doppler creates a "swishing" sound, which is the sound of your blood moving through the arteries and veins.

Sometimes during a duplex ultrasound, the health care provider may calculate an ankle-brachial (ABI) index. You will need to wear blood pressure cuffs on your arms and legs for this test.

The ABI number is obtained by dividing the blood pressure in the ankle by the blood pressure in the arm. A value of 0.9 or greater is normal. An ABI of less than 0.5 is linked to peripheral vascular (arterial) disease.

Usually, there is no preparation for a duplex ultrasound.

If you are having an ultrasound of your stomach area, you may be asked not to eat or drink after midnight. Tell the person doing the ultrasound exam if you are taking any medicines, such as blood thinners, that might affect the results of the test.

You may feel some pressure as the wand is moved over the body, but there is usually no discomfort.

Duplex ultrasound is a less-invasive option to arteriography and venography. A duplex ultrasound can show how blood flows to many parts of the body. It can also tell the width of a blood vessel and reveal any blockages.

A duplex ultrasound can help diagnose the following conditions:

• Abdominal aneurysm
• Arterial occlusion
• Blood clot
• Carotid occlusive disease (See: Carotid duplex)
• Renal vascular disease
• Varicose veins
• Venous insufficiency

A renal duplex ultrasound can also be used after transplant surgery to see how well a new kidney is working.

A normal result is normal blood flow through the veins and arteries. There is normal blood pressure and no sign of a narrowing or blockage of a blood vessel.

An abnormal result depends on the specific area being examined. An abnormal result may be due to a blood clot or plaque build-up in a blood vessel.

There are no risks.

Cigarette smoking may change the results of an ultrasound of the arms and legs because nicotine can cause the arteries to shrink (constrict).

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Grainger RC, Allison D, Adam, Dixon AK. Diagnostic Radiology: A Textbook of Medical Imaging. 4th ed. Orlando, Fl: Churchill Livingstone; 2001:60, 1684.