An ABI ultrasound is a quick, painless test that compares blood pressure in your ankles to blood pressure in your arms to check for peripheral artery disease (PAD), a condition where narrowed arteries reduce blood flow to your legs. The “ultrasound” part refers to a small handheld Doppler probe used to listen for blood flow in your arteries during the test. It’s typically the first screening tool used when PAD is suspected.
How the Test Works
The test combines standard blood pressure cuffs with a handheld Doppler ultrasound device. You lie flat on your back while a technician or provider takes blood pressure readings in both arms and both ankles. Instead of using a stethoscope to listen for your pulse (as in a regular blood pressure check), they apply a small amount of ultrasound gel to your skin and use the Doppler probe to detect blood flow through your arteries. The probe picks up the sound of moving blood, which helps pinpoint exactly when flow resumes as the cuff deflates.
For the ankle readings, the cuff goes just above your ankle bone. The provider checks two arteries in each foot: one on the top of the foot and one behind the inner ankle bone. They inflate the cuff until the blood flow signal disappears, then slowly release it at about 1 mmHg per second until the signal returns. That point marks your systolic blood pressure in that artery. The whole process takes roughly 15 to 20 minutes, requires no needles or contrast dye, and involves no special preparation.
What the ABI Number Means
Once all measurements are taken, a simple ratio is calculated for each leg. The higher of the two ankle artery pressures is divided by the arm pressure. In a healthy person, blood pressure at the ankle should be about the same as or slightly higher than in the arm, giving a ratio near 1.0.
An ABI below 0.9 is considered abnormal and indicates some degree of artery narrowing in that leg. The further below 0.9 the number falls, the more significant the blockage. Values between 0.5 and 0.9 generally suggest mild to moderate disease, while anything below 0.5 points to severe restriction. On the other end, a reading above 1.3 can signal that the arteries are unusually stiff or calcified, which makes the test less reliable (more on that below).
Why It’s Done
PAD develops when fatty deposits build up inside artery walls, gradually narrowing the channel blood flows through. The legs are most commonly affected. Classic symptoms include cramping or pain in the calves, thighs, or hips during walking that goes away quickly with rest. Some people also notice slow-healing wounds on their feet, coldness in one leg compared to the other, or changes in skin color.
Beyond leg symptoms, PAD is a marker of widespread artery disease. An abnormal ABI is linked to higher risk of heart attack, stroke, and cardiovascular death, because the same plaque buildup happening in the legs is often happening elsewhere. That’s why the test carries significance beyond just diagnosing leg pain. It can provide a window into overall cardiovascular health.
Your provider is more likely to order an ABI if you have risk factors for PAD: a history of smoking, diabetes, high blood pressure, high cholesterol, or known plaque buildup in other arteries. It’s worth noting that the U.S. Preventive Services Task Force currently says there isn’t enough evidence to recommend routine ABI screening in adults who have no symptoms, so the test is typically reserved for people who either have leg complaints or carry significant risk factors.
Where the Test Falls Short
The ABI is a screening tool, not a detailed map of your arteries. It tells you whether blood flow to the legs is reduced, but it can’t pinpoint exactly where a blockage is or how long the narrowed segment is. Its sensitivity also drops for blockages isolated to a single artery below the knee, because the test relies on whichever ankle artery gives the higher reading.
People with diabetes or advanced age present a particular challenge. Calcium deposits can stiffen the artery walls, making them harder to compress with a cuff. This artificially inflates the pressure reading and can produce a falsely normal or even high ABI, masking real disease underneath. A study looking at people with type 1 diabetes found that while an ABI above 1.3 almost always indicated calcified arteries (99% specificity), it missed the vast majority of people who actually had calcification (only 14% sensitivity). In these cases, providers may use alternative tests, such as a toe pressure measurement, since the small arteries in the toes are less prone to calcification.
ABI vs. Full Arterial Ultrasound
The term “ABI ultrasound” sometimes causes confusion with a full arterial duplex ultrasound, which is a different and more involved exam. An ABI uses a simple Doppler probe only to detect blood flow signals for pressure readings. A duplex ultrasound, by contrast, creates real-time images of artery walls and measures blood velocity at multiple points along the leg. Duplex scans evaluate arteries from the pelvis all the way down to the foot, checking each segment for narrowing or blockages. Lesions causing 50% or greater narrowing are typically flagged as significant.
Think of the ABI as a quick yes-or-no screening question: is blood flow to this leg reduced? A duplex ultrasound is the follow-up investigation that answers where, how bad, and how long the problem segment is. If your ABI comes back abnormal, a duplex scan is often the next step to guide treatment decisions.
What to Expect From Your Results
A normal ABI (roughly 1.0 to 1.3) is reassuring but doesn’t completely rule out early or mild disease. If your result is borderline, your provider may recommend repeating the test after exercise, since walking on a treadmill can unmask reduced blood flow that isn’t apparent at rest.
An abnormal result doesn’t automatically mean you need a procedure. Mild to moderate PAD is often managed with lifestyle changes: quitting smoking, structured walking programs, and managing blood pressure, cholesterol, and blood sugar. The ABI can also be repeated over time to track whether the disease is stable or progressing. For more severe cases, imaging and potential intervention become part of the conversation, but the ABI itself is just the starting point.