Patient Basics: Venous Ultrasound of the Legs (Lower Extremity Doppler)

Originally published by Harvard Health.

What is the test?

This type of ultrasound shows if there is a blockage in a leg vein. Such blockages are usually caused by blood clots, which can be dangerous and even life threatening if they break loose and travel through the blood to the lungs. If you have pain or swelling in one leg, your doctor may order an ultrasound to determine whether your symptoms are caused by a blockage.

How do I prepare for the test?

No preparation is necessary.

What happens when the test is performed?

After squirting some clear jelly onto the inside of one of your thighs to help the ultrasound sensor slide around easily, a technician or doctor places the sensor against your skin. Once it’s in place, an image appears on a video screen, and the technician or doctor moves the sensor up and down along your leg — from the groin to the calf — to view the veins from different angles. The examiner presses the sensor into your skin firmly every few inches to see if the veins change shape under pressure. He or she then checks your other leg in the same way. As the machine measures the blood flowing through a vein, it makes a swishing noise in time with the rhythm of your heartbeat. This test usually takes 15-30 minutes. Most people don’t feel any discomfort, but if your leg was swollen and sensitive to the touch before the test, the pressure of the sensor might cause some tenderness.

What risks are there from the test?

There are no risks.

Must I do anything special after the test is over?

No.

How long is it before the result of the test is known?

A radiologist reviews a recording of your ultrasound and checks for signs of blockages in the veins. Your doctor should receive a report within a few hours to a day.