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 of blood vessels to create pictures. Doppler looks at how sound waves reflect off moving objects, such as blood.

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.

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 move better. A wand, called a transducer, is moved over the area being tested. This wand sends out the sounds 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 bounce and 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.