Sudden loss of limb blood flow is an emergency
Do Not Wait for a Routine Scan if a Leg Suddenly Changes
Go for immediate emergency assessment if a leg or foot suddenly becomes:
- Severely painful, especially when the pain began abruptly.
- Pale, blue, mottled or noticeably colder than the other side.
- Numb, tingling, weak or difficult to move.
- Without a previously felt pulse, particularly after a vascular procedure or with an irregular heartbeat.
Seek urgent vascular or medical assessment for:
- Persistent foot pain at rest, especially at night or when lying flat.
- A new black or dusky toe, rapidly worsening wound, spreading infection or foul-smelling discharge.
- A foot ulcer that is not healing, particularly with diabetes, reduced sensation or absent pulses.
- Sudden worsening of pain or circulation after angioplasty, stenting or bypass surgery.
Acute limb ischaemia can threaten the limb within hours. Emergency assessment and treatment should not be delayed while arranging a routine outpatient arterial Doppler.
What is Lower-Limb Arterial Duplex Ultrasound?
A handheld probe sends sound waves through gel on the skin. Grey-scale imaging shows the artery walls, lumen and plaque. Colour Doppler displays moving blood, while spectral Doppler creates a waveform and measures velocity at multiple points along the artery.
A narrowing accelerates blood through a smaller channel and alters the waveform beyond it. By comparing velocity, waveform shape and colour-flow appearance between segments, the radiologist can locate and estimate the significance of stenosis or occlusion without an injection or ionising radiation.
PAD is More Than a Leg Problem
Peripheral arterial disease commonly reflects atherosclerosis affecting the whole circulation. A scan maps leg blood flow, but the treating clinician also addresses cardiovascular risk—including smoking, diabetes, blood pressure and cholesterol—because heart attack and stroke risk may be increased.
How Do Arterial Duplex, ABPI and Angiography Differ?
These tests complement rather than simply replace one another. The choice depends on symptom severity, examination, ABPI, kidney function, diabetes, previous procedures and whether treatment is being planned.
Why Might the Scan Be Requested?
Other indications can include:
- Suspected peripheral arterial disease in a person with diabetes or other vascular risk factors.
- Unexplained leg pain when arterial disease is one possible cause.
- Assessment before applying strong compression for a leg ulcer or venous disease.
- Planning for angioplasty, stenting, endarterectomy or bypass surgery.
- Follow-up of a known arterial stenosis, occlusion or aneurysm.
- Checking patency after angioplasty, stenting, bypass grafting or another vascular procedure.
- Suspected pseudoaneurysm after arterial puncture or catheterisation.
- Surveillance of a bypass graft or stent according to a vascular programme.
Back, hip, joint, nerve and muscle disorders can also cause walking pain. Ultrasound findings are interpreted alongside pulse examination, symptom pattern and functional limitation.
Which Arteries and Measurements Are Examined?
How Should I Prepare?
Follow the booking instructions for the exact scan. A routine groin-to-ankle examination usually needs little preparation, but abdominal or pelvic arterial views can be affected by bowel gas.
- Bring the referral and previous ABPI, arterial Doppler, CTA, MRA or angiography reports.
- Bring details of any angioplasty, stent or bypass—including side and date—plus an accurate medicine list.
- Tell the team about diabetes, kidney disease, wounds, infection, dressings or severe rest pain.
- Do not apply heavy moisturiser or oily cream to the legs immediately before the scan if this can be avoided.
- Ask for individual advice if fasting conflicts with diabetes treatment, pregnancy, frailty or another medical condition.
What Happens During the Arterial Duplex?
The radiologist confirms the affected side, walking distance, rest pain, wounds, risk factors, previous arterial procedures and the treatment question the scan must answer.
Shoes, socks and relevant clothing are removed. You usually lie on your back, with position adjusted for the groin, behind-knee and calf arteries.
The probe follows the arteries from the groin towards the ankle. Gentle pressure is required for contact but arterial duplex does not use the repeated firm vein compression used in a DVT scan.
The radiologist samples blood flow at standard points and any suspected narrowing. You may hear amplified pulsing or “whooshing” sounds generated by the Doppler signal.
Blood-pressure cuffs around the arms and ankles may inflate firmly for a short time. Toe pressures or an exercise test are separate additions when clinically appropriate and available.
Representative images, waveforms and velocities are saved. The formal report identifies disease distribution and whether further vascular assessment or imaging is advised.
A complete examination commonly takes about 30–60 minutes. Bilateral scans, bypass surveillance, abdominal views or extensive calcification can take longer.
What Does an ABPI Measurement Mean?
The ankle–brachial pressure index compares systolic blood pressure at the ankle with the highest arm pressure. It helps estimate whether arterial pressure reaching each foot is reduced. Pulse examination, foot appearance and Doppler signal quality remain part of the assessment.
Do not use an isolated ABPI value to choose compression strength or decide that a wound has adequate blood supply. The treating clinician interprets the complete vascular assessment.
What Do Common Report Terms Mean?
What Can Arterial Doppler Not Determine Reliably?
- Every small foot or skin vessel involved in microcirculation and wound healing.
- Complete aortic and iliac anatomy when bowel gas, depth or body habitus limits ultrasound.
- The full lumen behind dense calcification that blocks the returning sound waves.
- All causes of walking pain, rest pain, numbness or a non-healing wound.
- Whether a person needs angioplasty or bypass without clinical and functional assessment.
- A complete treatment road map when long occlusions or multilevel disease require CTA, MRA or angiography.
- Accurate ABPI interpretation in every patient with non-compressible calcified ankle arteries.
- All arterial segments when wounds, dressings, severe pain, swelling or limited mobility restrict probe access.
A technically limited or apparently normal scan does not dismiss concerning rest pain, tissue loss or abnormal pulses. Further vascular assessment, toe pressures, exercise testing or angiographic imaging may be required when the clinical picture and ultrasound do not agree.
What Happens After the Scan?
The gel is wiped away and you can usually return to normal meals, medicines and activity. The radiologist prepares a report describing disease distribution, severity, limitations and any treated segment assessed.
Urgent limb-threatening findings are communicated through the appropriate pathway. Planned findings are reviewed by the referring or vascular clinician, who combines them with symptoms, wounds, ABPI, walking limitation, cardiovascular risk and treatment suitability.
Possible next steps include risk-factor treatment, supervised exercise, wound care, podiatry, additional CTA or MRA, vascular review or revascularisation. Do not start compression, stop antiplatelet medicine or change exercise plans solely from a report without clinical advice.
Myth vs Fact
Frequently Asked Questions
Do I need to fast for an arterial Doppler?
Usually not for a leg-only examination. If the abdominal aorta or iliac arteries are included, a light meal or short fasting period may be advised. Follow your booking instructions and call if fasting is unsafe.
Should I stop an antiplatelet or blood-thinning medicine?
No. Do not stop prescribed antiplatelet or anticoagulant medicine for an external ultrasound unless your treating clinician specifically instructs you. Bring an accurate medicine list.
Is the scan painful?
It is usually painless. Probe pressure may be uncomfortable over a wound or painful area, and ABPI cuffs squeeze the arms and ankles briefly. Tell the radiologist if you need an adjustment.
Will both legs be scanned?
The referral determines whether one or both legs require a full arterial map. Both sides may be compared even when symptoms are worse on one side, but this is not automatic for every appointment.
What is the difference between arterial and venous Doppler?
Arterial Doppler assesses blood travelling from the heart to the legs and looks for narrowing or blockage. Venous Doppler assesses blood returning to the heart and looks for DVT or venous reflux.
Is ABPI the same as an arterial duplex?
No. ABPI is a pressure ratio providing a functional overview. Duplex shows named arteries and measures blood-flow velocity to locate disease. They are often used together.
Why can ABPI be misleading in diabetes?
Diabetes can make ankle-artery walls stiff and difficult to compress, producing a normal or high value despite disease. Toe pressures, waveforms or imaging may be needed when clinical concern remains.
Can ultrasound replace CT angiography?
Sometimes duplex supplies all the information needed. Complex, deep, calcified or multilevel disease may still need CTA, MRA or catheter angiography for complete treatment planning.
When will I receive the result?
The radiologist prepares a report for the referring clinician. Urgent findings are communicated through the appropriate pathway. Ask before leaving how and when the result will be discussed.