Different tests answer different questions. Knowing which question your clinician is asking makes the results far easier to understand — and makes it obvious why a single number cannot settle everything.
The main tests, and what each one is for
| Test | Question it answers | What it involves |
|---|---|---|
| Ankle-brachial index (ABI) | Is blood pressure at the ankle lower than at the arm — i.e. is there arterial narrowing? | Blood pressure cuffs and a handheld Doppler. Minutes, no needles. |
| Toe-brachial index (TBI) | Same question, when ankle vessels are too stiff for the ABI to be reliable | A small cuff on the big toe. Used routinely in diabetes and kidney disease. |
| Exercise ABI | Does the pressure drop when demand rises, even if the resting number looks normal? | ABI before and after walking on a treadmill. |
| Arterial duplex ultrasound | Where exactly is the narrowing, and how severe? | Ultrasound probe and gel, no radiation. |
| Venous duplex ultrasound | Is there a clot? Are the vein valves leaking? | Same technology, different protocol — and it will not be run correctly unless the right question is asked. |
| CTA / MRA | Detailed road map before a procedure | CT or MRI with contrast. Kidney function matters for the choice. |
| Angiography | Definitive mapping, usually at the time of treatment | Catheter-based, in a procedure suite. |
Arterial and venous ultrasound are not the same scan
This trips people up constantly. “I had an ultrasound of my leg and it was fine” does not say which question was asked. A venous duplex looking for a clot is a different study from an arterial duplex looking for narrowing. If you are unsure which you had, it is a reasonable thing to ask — and worth knowing before assuming your arteries have been checked.
Why one measurement cannot rule out vascular disease
An ABI is a good test, not a perfect one. In people with diabetes, chronic kidney disease, or long-standing disease, calcium in the vessel wall makes the ankle arteries hard to compress — and a hard artery gives a falsely high reading. That is why a normal or high ABI in someone with symptoms is a reason for more testing rather than reassurance, and why the toe pressure is often the more trustworthy number in those groups.
Home pulse oximeters, smart-watch readings and consumer “circulation checkers” do not substitute for any of this. They measure something, but not the thing that diagnoses arterial disease.
Reading results in context
Numbers mean different things depending on who they belong to. The same ABI carries different weight in a 45-year-old non-smoker with no symptoms than in a 70-year-old with diabetes and a toe wound. And results almost never stand alone — the history, the examination, the wound if there is one, and the other conditions all feed into what happens next. If a number has been given to you without an explanation of what it means for you specifically, asking for that explanation is entirely reasonable.
Test guides
- ABI and TBI tests: what to expect and what results mean
- Arterial and venous ultrasound: different tests for different questions
- Vascular imaging: ultrasound, CT, MR and angiography
- Preparing for the appointment
Common questions
Does an ABI hurt?
No more than a blood pressure check. Cuffs inflate on the arms and ankles and a small Doppler probe listens to the pulse. The whole thing usually takes ten to fifteen minutes and needs no preparation beyond being able to lie flat for a few minutes.
Do I need to fast or stop my medicines?
Not for an ABI or a routine duplex ultrasound. CT or MR angiography involves contrast, so there may be instructions about kidney function, metformin, or fasting — the department performing it will tell you, and it is worth asking when you book rather than on the day.
My ultrasound was normal but my leg still hurts. What now?
Go back. A normal scan narrows the possibilities rather than ending the conversation — and it is worth confirming which scan was done and which question it answered. Symptoms that persist without explanation deserve another look, not a shrug.
Can my podiatrist do these tests?
It varies by practice. Some podiatry offices have ABI equipment and Doppler, others refer for vascular studies. Rather than assume either way, ask the specific practice what they can do in-house before the visit.
Where to go next
Sources
- National Heart, Lung, and Blood Institute. Peripheral Artery Disease — Diagnosis.
- American College of Cardiology. 2024 Lower Extremity PAD Guideline.
- Society for Vascular Surgery. Peripheral Artery Disease.
- NHS. Deep vein thrombosis.
Written by Tom Biernacki, DPM, FACFAS. Published 20 September 2026. General education, not medical advice.