A normal ankle-brachial index runs from 1.00 to 1.40. At 0.90 or below, the arteries feeding that leg have narrowed enough to drop the pressure at the far end. Above 1.40 the figure is not a result at all, because the cuff could not compress the artery enough to measure anything.
That last band is the one people are rarely told about, and it is why a printout showing 1.5 can carry worse news than one showing 0.85. The test takes about twenty minutes, involves nothing sharper than a blood pressure cuff, and produces one number for each leg that shapes decisions well beyond the leg. This guide covers what the number measures, how each band is read, when a reassuring figure should not be believed, how the result changes what treatment is safe, and who should be asking for the test.
On this page
- What counts as a normal ankle-brachial index?
- What the number is actually measuring
- Reading the five bands
- When a normal reading is not reassuring
- How the result changes treatment
- What happens during the test
- What to avoid
- Living with a borderline result
- Who should ask for the test
- Questions about the test
- The takeaway
What counts as a normal ankle-brachial index?
Between 1.00 and 1.40, taken with the person lying flat and rested.
A figure in that range means blood pressure at the ankle is at least as high as blood pressure in the arm, which is what a healthy leg artery should manage. Pressure rises slightly on the way down the body, so a small margin above 1.00 is expected and signals nothing unusual.
From 0.91 to 0.99 the reading is called borderline. It is not a diagnosis, and it is not a clean pass either, so it usually earns a repeat measurement or a walking test.
At 0.90 or below, narrowed arteries are reducing the volume of blood arriving in that limb. Clinicians call the underlying condition peripheral artery disease, and the index can identify it in someone who has never noticed a symptom.
Each leg gets its own number, and clinicians usually shorten the whole thing to ABI in conversation and on paperwork. A result of 1.10 on the right and 0.72 on the left is a common and entirely meaningful pattern. Averaging the two would bury the leg that needs attention, so ask for both figures separately.
What the number is actually measuring
A ratio, not a pressure. The ankle-brachial index divides the systolic blood pressure measured at the ankle by the systolic pressure measured at the arm, which is why it carries no units and lands somewhere near 1.
Systolic pressure is the top figure in an ordinary blood pressure reading, the peak produced as the heart contracts. Measured at the arm it shows what the heart is generating; measured at the ankle it shows how much survives the trip down the leg.
Comparing the two is what makes the test work. An ankle pressure of 100 mmHg means nothing by itself: in someone whose arm pressure is 110 it is unremarkable, and in someone whose arm pressure is 180 it is a serious finding. Dividing one by the other strips out the person’s general blood pressure and leaves the leg.
Two arteries are sounded at each ankle, one behind the inner ankle bone and one across the top of the foot, and the higher of those figures represents that leg. Both arms are measured too, and the higher arm pressure becomes the denominator. Guidance from the National Heart, Lung, and Blood Institute places the ankle-brachial index first in the sequence of tests used to diagnose peripheral artery disease, and its position there explains the design: quick, cheap, repeatable, and accurate enough to decide whether anything more involved is warranted.
What the number cannot do is locate anything. It reports that flow into the limb is reduced, not where the narrowing sits or how long a stretch it covers. Those questions belong to ultrasound imaging, ordered once the index has established there is something worth looking for.
Reading the five bands
Five bands, and only two of them are straightforward.
How an ankle-brachial index result is read
| Reading | Usually means | What follows |
|---|---|---|
| Above 1.40 | Artery will not compress | Measure at the toe |
| 1.00 to 1.40 | Normal supply | Look elsewhere for the cause |
| 0.91 to 0.99 | Borderline | Repeat, often after walking |
| 0.41 to 0.90 | Reduced flow | Vascular review |
| 0.40 or below | Severely reduced flow | Prompt specialist referral |
One number per leg. A figure above 1.40 is not a high score, it means no valid pressure could be obtained.
The normal band, 1.00 to 1.40, says arterial supply to that leg is adequate. Where a foot wound refuses to close on a leg measuring in this range, the obstacle sits somewhere else: pressure on the wound, infection, swelling, glucose control, or a problem on the vein side. Pressure is the most frequently missed of those, and the devices used to take it off a wound appear in our article on offloading a diabetic foot ulcer.
Borderline, 0.91 to 0.99, splits into two groups: people with early disease a resting measurement cannot yet detect, and people who simply measure there and stay there. Walking is what tells them apart.
From 0.41 to 0.90 the finding is established, and the figure tends to track with what the person feels. Readings near the top of the band often accompany cramp on walking and nothing more, while readings near the bottom show up alongside pain at rest and wounds that stay open month after month.
At 0.40 or below the leg is severely short of blood. A number down here alongside an open wound or night pain is treated as a limb at risk and goes to a vascular team promptly, because restoring flow determines everything that follows. What these wounds look like, and why they behave so unlike other leg ulcers, is described in our article on arterial ulcers and ischemia.
Above 1.40 is not a good result. The cuff never squeezed the artery closed, so no valid pressure was captured and the ratio calculated from it means nothing. That is the single most misread thing about this test, and it deserves its own section.
When a normal reading is not reassuring
An index of 1.3 on a cold, pulseless foot is a contradiction, and the foot is the half telling the truth.
Arteries can stiffen. Calcium builds up in the middle layer of the artery wall, a separate process from the plaque that narrows the channel, and a flexible tube slowly becomes closer to rigid pipe. A cuff works by squeezing an artery shut and detecting the point where flow returns, so a hardened vessel has to be pumped well beyond its true pressure before it closes, and the recorded figure comes out too high.
The result looks normal, or better than normal, on a limb whose circulation is genuinely poor. Long-standing diabetes and chronic kidney disease are where this happens most, and advanced age contributes. Anything above 1.40 is reported as uninterpretable for that reason, but the real trap is the reading landing at 1.15 on a leg whose true index would have been 0.7. High enough to look fine, not high enough to trigger the warning.
The mismatch is the clue. A comfortable number on a foot that is cold, hairless, pulseless or carrying a wound that will not close deserves a second measurement by another method, particularly in someone with diabetes or kidney disease.
The usual answer is to measure at the toe instead. Small toe arteries mostly escape the hardening, so a miniature cuff around the big toe gives a pressure that can be trusted where the ankle cannot. The toe-brachial index is read on its own scale, with roughly 0.70 as the dividing line, and a normal ankle figure sitting next to a low toe figure settles the argument.
A resting measurement also misses disease that only declares itself under load. A leg can supply enough blood for someone sitting still and fall short the moment the muscles ask for more, which is what produces cramping after a fairly predictable walking distance. Where the story fits and the resting figure does not, the test is repeated after a few minutes on a treadmill. A fall of roughly a fifth or more from the resting value is treated as abnormal, and that drop is often the only objective evidence in a person whose resting number reads 0.95.
How the result changes treatment
Four decisions hang on the ankle-brachial index, which is why a wound clinic wants it before committing to much else.
The first is compression. Firm bandaging closes wounds caused by failing leg veins, and the same bandaging on a leg whose arteries have narrowed squeezes down on a supply that is already thin. Since the two wound types can appear in similar places and look broadly alike, the index is what separates a treatment from an injury. Services commonly take 0.8 and above as the point where standard compression can usually be applied, use reduced strength under specialist supervision through roughly the 0.5 to 0.8 range, and hold off below that. What distinguishes one ulcer from another before any measurement is taken is laid out in our comparison of the main leg ulcer types.
The second is what healing can realistically achieve. A wound on a leg measuring around 0.5 or lower is unlikely to close on dressings alone, since the repair needs a supply the leg does not currently have. Establishing that early redirects the plan from refining the dressing to answering the supply question, and saves months of reasonable-looking treatment that was never going to work. On a diabetic foot, the higher grades of the system used to describe these wounds are defined by tissue that has died from lost blood supply, as set out in our guide to diabetic foot ulcer grades.
The third is timing. An index of 0.85 in someone with cramp on walking and no wound is managed with medication, walking programs and risk factor treatment. The same 0.85 on a leg carrying an open ulcer, or any figure below 0.5, moves the vascular referral to the front of the queue.
The fourth has nothing to do with the leg. A low index marks arterial disease throughout the body, because someone whose leg arteries have narrowed measurably usually has the same process underway in the vessels supplying the heart and the brain. Cholesterol treatment, blood pressure control and antiplatelet medication are frequently offered on that basis, and the number is often what opens the conversation.
What happens during the test
An ankle-brachial index takes about twenty minutes. Nothing is injected and nothing pierces the skin.
You lie flat on your back, usually for five to ten minutes before anything is recorded, since standing or sitting beforehand shifts the pressures. Shoes and socks come off and sleeves go up.
A standard blood pressure cuff goes on the upper arm and is inflated. In place of a stethoscope, a small handheld probe rests against the skin over the artery, sending an ultrasound signal into the vessel and turning the returning echo into an audible whoosh in time with the heartbeat. The cuff is inflated until that sound disappears, then released slowly until it returns, and the pressure at that moment is the systolic reading. The same is repeated on the other arm, then with the cuff moved to just above each ankle, sounding two arteries per foot. Six readings altogether, from which two indices are calculated.
The cuff squeeze is firm but brief, and the discomfort is much the same as any blood pressure check. Say in advance if there is an open wound or recent surgery on the leg, since a cuff is not placed over a wound and the measurement is taken differently or postponed where that cannot be avoided.
Ask for the actual figures before you leave. “Your circulation is fine” is a summary; knowing the numbers were 1.12 and 0.94 gives you something to carry to the next appointment and compare against, which is how a slow change gets noticed at all.
What to avoid
Do not buy compression stockings on the strength of a figure you found online or heard mentioned in passing. The threshold that makes compression safe applies to a measurement taken on you, reasonably recently, on the specific leg being bandaged. That last part is the operative one, since the two legs frequently differ by more than people expect.
Do not try to reproduce the test at home with an automatic blood pressure monitor. Household cuffs are built for arms and use a different detection method, they perform badly on legs and worse on stiffened arteries, and a homemade figure has produced false reassurance often enough to count as a hazard.
Do not treat one reading as permanent. Arteries change, and a result from three years ago says very little about the leg today, particularly where new symptoms have appeared since.
Do not dismiss what you are feeling because the number came back normal. A calcified artery and disease that only shows under exertion can both hide behind a comfortable figure. If the foot is cold, painful at night, or carrying a wound that has not moved in a month, say so again even after a reassuring result.
And do not stop at the leg. A low index is a whole-body finding, so treating it purely as a foot problem misses the reason cholesterol and blood pressure medication were offered alongside it.
Living with a borderline result
Borderline is a hard place to sit. Nothing has been diagnosed and nothing has been ruled out, and the advice arriving with it, walk more and come back in a year, feels thin against the worry that prompted the test.
The band is a genuine holding position, not a gentle way of delivering bad news, and plenty of people sit in it for years without moving. What changes the picture is symptoms, so the practical job is noticing them: the distance you manage before the calf tightens, whether that distance is shrinking, whether the foot has started to feel cold or ache in bed.
The distance one is easy to miss, because the adjustment happens quietly. People take the car for a trip they used to walk, pause at the top of the hill to look at their phone, and choose the near parking space without registering the choice. Writing down what you manage this month turns a vague sense of slowing down into a fact a clinician can act on.
Then there is the fear sitting behind the appointment. People arrive for an ankle pressure measurement having read about limb loss the night before, and leave with a number nobody explained. Ask what your figure was, which band it falls in, and what would have to change for the plan to change. A specific answer about your own leg is usually less frightening than whatever you had been picturing.
A second group deserves mentioning: the people who get a normal result and come away feeling dismissed, because the leg still hurts and the test said nothing was wrong. A normal ankle-brachial index rules out one cause. Spinal narrowing, joint disease, nerve pain and vein problems all produce leg pain, and none of them register here. A normal figure should redirect the search, not close it.
Who should ask for the test
Anyone with a wound on the foot or lower leg that has not healed within a month should have the circulation into that limb measured before another dressing plan is written. That one rule catches most of the people who need an ankle-brachial index and are not being offered one.
It applies equally to leg pain that arrives on walking and settles on stopping, to a foot that aches at night and eases when it hangs toward the floor, to feet that stay cold or change color with position, and to anyone about to start compression bandaging on a leg wound.
Beyond that, testing is reasonable to raise with a clinician in people over about 65, and earlier in anyone with diabetes, a smoking history, kidney disease, or known heart and artery disease elsewhere. The condition stays silent in a great many people until something breaks the skin, and a number is the only way to find it before that point.
A limb that turns suddenly cold, white or numb with severe pain needs emergency assessment and should not wait for any measurement. Tissue turning black, red streaking traveling up the leg, or a fever alongside a foot wound need same-day attention. Flow that has failed completely is measured against a clock, not a calendar.
Questions about the test
Does the ankle-brachial index test hurt?
No. The only sensation is a cuff tightening, once on each arm and once above each ankle, along with cool gel where the probe touches the skin. The cuff can feel tight for a few seconds where an artery is stiff, since it has to be inflated higher than usual, and that is worth mentioning to whoever is taking the reading.
Can I have peripheral artery disease with a normal ABI?
Yes, in two situations. Stiffened arteries, common with long-standing diabetes and kidney disease, push the reading up and can mask genuinely poor flow. The other is disease that only appears under exertion, since a leg may cope at rest and fall short during a walk. Symptoms that do not match a normal figure should be reported, because a toe pressure or a walking test can resolve the disagreement.
What does an ankle-brachial index of 1.5 mean?
It means no usable measurement was obtained on that leg. The artery would not compress under the cuff, so the pressure recorded was the pressure needed to flatten a hardened vessel and not the pressure inside it. A figure like this calls for a different method, usually a toe pressure, and carries no reassurance about the blood supply either way.
How often should an ankle-brachial index be repeated?
No single interval suits everyone. Timing depends on the first result, on whether symptoms are present or changing, on whether a wound is being treated, and on what other conditions are in play. A new or worsening symptom justifies remeasuring regardless of when the last reading was taken, and a leg being treated with compression is usually reassessed periodically.
Can an ankle-brachial index improve?
It can rise noticeably after a procedure that reopens or bypasses a narrowed artery, and a repeat measurement is one way the success of that procedure is judged. Stopping smoking, supervised walking programs and treatment of cholesterol and blood pressure aim at slowing the disease and improving what a person can do. Walking distance often improves more than the number does, which is useful to know before treating an unchanged index as a failure.
Is this the same as a Doppler ultrasound scan?
Not quite. The handheld probe used here is a Doppler device, so the words overlap, but this test produces a pressure ratio and no pictures. A duplex ultrasound scan is a separate, longer examination that images the arteries and shows where a narrowing sits and how tight it is. The index generally comes first, and the scan follows when a procedure is being considered.
The takeaway
A normal ankle-brachial index is 1.00 to 1.40. Borderline runs from 0.91 to 0.99, disease is established at 0.90 and below, and 0.40 or under marks a leg severely short of blood. Each leg carries its own number, so ask for both.
The band people misread is the one at the top. A figure above 1.40 is not an excellent score, it is a failed measurement on an artery too stiff to compress, and the same stiffening can lift a genuinely poor leg into a range that looks normal. Where the number and the foot disagree, the foot is usually right, and a toe pressure will say so.
For a wound that is not closing, this one measurement decides whether compression is safe, whether dressings alone have any prospect of working, and how quickly a vascular opinion is needed. A leg wound dressed month after month without anyone measuring the pressure behind it is the appointment worth asking for.
Has the circulation to that leg ever been measured?
A wound that has stalled deserves a pressure reading before the next dressing change is planned. An assessment can establish what the supply is doing, whether compression is safe on that leg, and whether a vascular referral is the right next step.
Ankle pressure measurement, the compression decision that follows it, and referral onward when flow needs restoring all sit inside our chronic wound treatment service, alongside the dressing work on a lower limb wound that has stopped improving.
This article is general education and does not replace a clinical assessment. Index values and the thresholds described here are interpreted alongside the examination, the symptoms and the person’s other conditions, and no figure on this page should be used to start, adjust or rule out compression on your own. A limb that becomes suddenly cold, pale or severely painful needs emergency care, not a measurement.
