Duplex Doppler scan

A duplex Doppler scan is a type of ultrasound that does two things at once. It shows a picture of the blood vessel, and it measures the speed and direction of blood flowing through it. Colour on the screen shows which way the blood is moving.

The scan is painless and uses sound waves, not radiation, so it can be repeated as often as needed. A small probe with cool gel is moved over the skin. You may hear a whooshing sound, which is your blood flow.

Most decisions in vascular surgery start with this scan. It shows whether a vein is leaking, an artery is narrowed or a clot is present, and you can see the images with the doctor as they are explained.

Your doctor may suggest a Doppler scan if you have:

Varicose veins, leg heaviness, ankle swelling or skin changes around the ankle

A swollen, painful leg or arm where a clot is suspected

Calf pain on walking, cold feet or weak foot pulses

Diabetes with numbness, a wound or colour change in the foot

A recent mini-stroke or stroke, or a narrowing heard in the neck arteries (carotid duplex)

A need for dialysis access, or a fistula that is not working well

A known aortic aneurysm that needs regular measuring

It is also used before and after vascular procedures, to plan treatment and to check that stents, bypasses or treated veins are working.

The scan is done in the clinic and usually takes 15–30 minutes, depending on how many vessels are checked.

You will lie on a couch, or stand for a vein reflux study, because leaking valves show best when you are upright. Gel is applied and the probe is pressed gently over the vessels. For a vein study, the doctor may squeeze your calf briefly to test the valves. For an arterial study, blood pressure cuffs on your ankles and arms may be used to measure the ankle–brachial index (a blood pressure comparison between ankle and arm).

How to prepare:

Wear loose, comfortable clothing that is easy to roll up or remove

For leg and arm scans, no special preparation is needed

For a scan of the abdomen or aorta, you may be asked not to eat for a few hours

Bring previous scans, reports and your medicines list

Different scans answer different questions:

Venous reflux study: shows which vein valves are leaking and where, which guides varicose vein treatment.

Venous scan for clots: shows whether there is a clot in the deep or surface veins, and how far it extends.

Arterial duplex and ABI: shows where leg arteries are narrowed or blocked and how much blood flow reaches the foot.

Carotid duplex: measures any narrowing in the neck arteries that supply the brain.

Fistula assessment: maps arm veins before access surgery and checks the flow and any narrowing in an existing fistula.

Aortic scan: measures the width of the abdominal aorta to find or follow an aneurysm.

Ultrasound has limits. Very stiff, calcified arteries, deep vessels or a lot of bowel gas can make some areas harder to see, and a CT scan is occasionally needed as well.

There is no recovery time. The gel is wiped off and you can go straight back to your normal activities, drive and eat as usual.

In most cases the doctor explains the findings during or right after the scan, at the same visit, and you can see the images on the screen. You will usually receive a written report that you should keep with your medical records.

If treatment is needed, the scan results form the basis of the plan. Some conditions, such as aneurysms, stents or fistulas, need repeat scans over time, so your doctor will tell you when the next one is due. Keep your reports and bring them to every visit, as comparing scans is often as useful as a single result.

Book a scan if you have leg aching, heaviness, swelling or visible veins, pain in the calf when walking, a foot wound with diabetes, or if your doctor has asked for a check of your arteries, veins or fistula.

Arrange a same-day scan if you have:

Sudden swelling and pain in one leg or arm

A fistula with a weak or absent thrill

Do not wait for a clinic scan. Go to the emergency department or call an ambulance if you have:

Sudden breathlessness, chest pain or coughing up blood

A leg or foot that suddenly becomes cold, pale, numb or very painful

Sudden severe abdominal or back pain, especially with a known aneurysm

Sudden weakness of the face, arm or leg, slurred speech or loss of vision