Most people leave the appointment with a number and no idea what it means. Someone says it is a bit low, or that it looks fine, and the conversation moves on to something else.
The number is worth understanding, because it is the one measurement in this whole area that is simple, repeatable, and yours. The National Heart, Lung, and Blood Institute puts it bluntly: be aware of your ABI, just as you know and keep track of your blood pressure numbers.
What follows is what each reading means, what to do when the number looks fine but the legs do not, what usually happens next, and why this particular figure says something about more than your legs. What the appointment itself involves is covered separately, so this stays on the result.
What the test actually measures
One sentence covers the mechanics. NHLBI describes the ankle-brachial index as the test that compares blood pressure in your ankle with the blood pressure in your arm, and calls it the test usually used first to diagnose peripheral artery disease.
That comparison is the whole idea. In a healthy leg the pressure at the ankle is at least as high as the pressure in the arm, because nothing is getting in the way. When an artery higher up has narrowed, the pressure that reaches the ankle falls, and the ratio between the two falls with it.
So the number is not a score and it is not a percentage. It is one pressure divided by another, which is why it has no units and why it sits near 1. What peripheral artery disease is explains the condition the number is looking for.
Ankle brachial index results: the five numbers
Every figure below is NHLBI’s, not a rule of thumb. Your own practice may use slightly different cutoffs, and the one that matters is the one the person reading your scan explains to you.
1. 1.00 or greater. NHLBI states plainly that a healthy ABI result is 1.00 or greater. The pressure reaching your ankle is as strong as the pressure in your arm, which is what it should be. If your legs are symptom free, this is the end of the conversation for now.
2. Between 0.90 and 1.00. This sits between the two figures NHLBI names, below the healthy result and above the threshold at which it says PAD may be present. It is not nothing and it is not a diagnosis. It is the reading most worth asking a direct question about, because what happens next depends on your symptoms and your risk factors rather than on the number alone.
3. Less than 0.90 at rest. NHLBI is specific: if you have an ABI of less than 0.90 while resting, you may have PAD. This is the number that turns a vague suspicion into something with a name, and it is the point at which treatment becomes a real conversation rather than a maybe.
4. Less than 0.40. NHLBI calls an ABI of less than 0.40 a sign of severe PAD. A reading this low alongside pain in the foot at rest, or a sore that will not close, is not something to sit on, and the section further down says why.
5. A number that cannot be trusted. Sometimes the ankle arteries will not compress properly under the cuff, which makes the reading unreliable rather than reassuring. NHLBI notes that a toe-brachial index is used when there are problems with the ankle arteries, measuring the pressure in the big toe instead, and that a TBI less than 0.7 is abnormal. If you were sent for a toe reading after an ankle one, this is why.
Worth writing yours down with the date. A single figure is a snapshot, and the useful information is usually the direction it moves over a few years.
When the result is normal and the legs still hurt
This is the situation people find most frustrating, and it has a straightforward answer.
A resting test measures a leg that is doing nothing. A narrowed artery can deliver enough blood for that and not enough for a leg climbing a hill, which is exactly why the symptoms arrive on the move. So the test is repeated after walking.
NHLBI describes the exercise version as showing the severity of your leg symptoms and the level of physical activity that produces them, and gives the figure that matters: a drop of 20 percent or more in a post-exercise ABI is abnormal. The CDC describes the same test as comparing ankle and arm pressures at rest and after exercise.
Two other things may be done alongside it. A six-minute walking test, which NHLBI describes as measuring how far you can walk in a hallway in six minutes, and segmental pressure testing, which checks different parts of the leg to work out where the narrowing sits rather than only whether it exists.
If your resting number was fine and your legs still stop you, ask whether an exercise test is appropriate. Pain that comes on when you walk and settles when you stop is the pattern that makes it worth asking.
What happens after an abnormal result
Less dramatic than most people expect, and a procedure is rarely the first move.
Walking is the treatment, not the thing to avoid. NHLBI describes supervised programs that run in a clinic or hospital, usually meeting at least three times a week, and home-based programs with coaching aiming at thirty minutes of continuous walking. This is counterintuitive when walking is what hurts, and it is still the first-line answer.
Medicines that protect more than the leg. NHLBI lists antiplatelet medicines such as aspirin or clopidogrel to prevent clots forming, along with statins and blood pressure medicines, and notes cilostazol may improve symptoms. Most of these are aimed at your arteries generally rather than at the ache itself.
Lifestyle changes, with smoking first. NHLBI lists quitting smoking, heart-healthy eating, a healthy weight, physical activity and stress management.
A procedure only when those are not enough. NHLBI is explicit about the order: if lifestyle changes, an exercise program, and medicines do not work well enough, a procedure or surgery may be recommended. What a leg artery procedure actually involves walks through the day, and who turns out to be a candidate is a separate question from what your number was. Treatment for poor leg circulation covers the options together, and how Medicare handles the cost is worth reading before anything is scheduled.
When a result needs acting on today
A low number on its own is a reason for an appointment. These are reasons not to wait for one.
- Pain in the foot that is there at rest, that wakes you at night, and that eases when you hang the foot out of bed
- A leg or foot that becomes suddenly cold, pale or blue and painful, which is an artery blocking rather than narrowing
- A sore or ulcer on the foot or toe that is not healing, is spreading, or is turning black
- Any wound on the foot in someone with diabetes that is not closing
- New numbness or weakness in the leg that comes on over minutes or hours
The second belongs in an emergency department the same hour. The first is rest pain, which means the blood supply is short even when the leg is doing nothing, and it is the point at which a low reading stops being something to monitor.
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Why the number matters above the knee
Here is the part that makes this worth understanding rather than filing away.
Narrowed arteries in the legs are rarely only in the legs. The CDC states that if you have PAD, you are at risk for developing coronary artery disease and cerebrovascular disease, which could lead to a heart attack or stroke. A low reading at the ankle is information about your arteries as a whole, which is why the medicines above are aimed at the whole system.
It also explains why the test gets offered to people whose legs feel fine. The CDC notes that up to 4 in 10 people with PAD have no leg pain, so a number can be the first and only sign that anything is going on.
If your reading was low and your legs feel normal, that is not a contradiction and it is not a reason to ignore it. Cold feet and changes in the color of the feet often show up before pain does, and a sore that will not heal is the sign that most often arrives too late to be called early.
Questions people ask about ankle brachial index results
What is a normal ankle brachial index result?
The National Heart, Lung, and Blood Institute says a healthy result is 1.00 or greater, meaning the blood pressure at your ankle is at least as high as the pressure in your arm. Below 0.90 at rest, it says you may have peripheral artery disease. A reading between those two figures sits in between, and what it means for you depends on your symptoms and risk factors rather than on the number by itself. Ask what yours was and write it down with the date.
My result was below 0.90. Does that mean I need a procedure?
Usually not, and rarely straight away. The National Heart, Lung, and Blood Institute puts procedures after lifestyle changes, a supervised or coached walking program, and medicines, and recommends one only when those have not worked well enough. A low number tells you something is narrowed. It does not tell you that opening it is the right next step, and for many people the walking program does more for how far they can go than anything else on the list.
Can my result be normal if I still get leg pain when walking?
Yes, and this is common enough to have its own test. A resting measurement looks at a leg that is doing nothing, and a narrowed artery can keep up with that while failing to keep up with a hill. The test is repeated after exercise, and the National Heart, Lung, and Blood Institute treats a drop of 20 percent or more afterward as abnormal. If your resting number was fine and your legs still stop you at a predictable distance, that is the test to ask about.
Why was I sent for a reading on my toe?
Because the ankle reading could not be relied on. In some people the arteries at the ankle do not compress properly under the cuff, which can make the number look better than the circulation actually is. A toe-brachial index measures the pressure in the big toe instead, and the National Heart, Lung, and Blood Institute treats a result below 0.7 as abnormal. Being sent for one is not a sign that something worse has been found, it is a sign that the first measurement was not trustworthy.
How often should the test be repeated?
There is no single schedule, and it depends on your result, your symptoms and your risk factors, so it is a question for the person who ordered it. What is worth doing yourself is keeping the figures. One reading is a snapshot and tells you where you are. Two or three readings a few years apart tell you the direction, which is far more useful, and almost nobody is given that information unless they have written the numbers down themselves.
So: ankle brachial index results are one pressure divided by another, 1.00 or greater is healthy, below 0.90 at rest raises peripheral artery disease, below 0.40 is severe, and a toe reading is used when the ankle cannot be trusted. A normal number with symptoms is a reason for an exercise test, not a dead end.
If you have not had the test and your legs are telling you something, a short symptom check takes about ninety seconds, and leg pain has several causes worth telling apart before you assume which one is yours.