An ABI, or ankle-brachial index, is a quick, painless test that compares blood pressure in your ankle to blood pressure in your arm. The ratio between these two numbers reveals how well blood is flowing to your legs. A normal ABI falls between 1.00 and 1.40, while a score of 0.90 or below signals peripheral artery disease (PAD), a condition where narrowed arteries restrict blood flow to the limbs.
How the Test Works
The test is simple. You lie on your back for 5 to 10 minutes to let your blood pressure settle. A healthcare provider then wraps a standard blood pressure cuff around each upper arm and each ankle, inflating them one at a time. Instead of using a stethoscope, they press a small handheld ultrasound device against your skin to listen for the pulse in each artery as the cuff deflates. The whole process takes only a few minutes, and you don’t need any special preparation beyond wearing loose clothing so the cuffs fit easily.
Blood pressure is measured at two arteries near each ankle and one in each arm. To calculate your ABI, the provider takes the higher of the two ankle readings and divides it by the higher of the two arm readings. Each leg gets its own score. For example, if the highest pressure at your right ankle is 120 mmHg and the highest arm pressure is 130 mmHg, your right ABI would be about 0.92.
What Your ABI Score Means
In a healthy circulatory system, blood pressure at the ankle is equal to or slightly higher than pressure in the arm, producing an ABI around 1.00 to 1.40. When arteries in the legs become narrowed by fatty plaque buildup, less pressure reaches the ankle, and the ratio drops.
- 1.00 to 1.40: Normal blood flow.
- 0.91 to 0.99: Borderline. May warrant monitoring or further testing.
- 0.90 or below: Indicates peripheral artery disease. The lower the number, the more severe the narrowing.
- Above 1.40: Considered unreliable because the arteries may be stiffened by calcium deposits, making them difficult to compress (more on this below).
An ABI of 0.90 or below has remained the diagnostic threshold for PAD in guidelines from the American Heart Association and American College of Cardiology, most recently reaffirmed in 2024.
Why the Test Matters Beyond Your Legs
A low ABI doesn’t just reflect poor circulation in your legs. It’s a strong warning sign for cardiovascular problems throughout your body. A large meta-analysis published in JAMA found that men with an ABI of 0.90 or below had a 10-year cardiovascular death rate of roughly 18.7%, compared to 4.4% in men with normal scores. Women showed a similar pattern: 12.6% versus 4.1%. That translates to roughly three to four times the risk of dying from a heart attack or stroke.
When the ABI drops even lower, below 0.60, the risk climbs further. Women in that range had about seven times the cardiovascular mortality of those with normal scores, and men about five and a half times. In other words, the ABI acts as a window into your overall arterial health, not just the arteries in your legs.
Who Should Get Tested
The classic symptom of PAD is an aching or cramping pain in the calf muscle during walking that goes away within about 10 minutes of rest. But many people with PAD have no symptoms at all, which is why screening guidelines exist for people at higher risk.
According to American and international guidelines, you should have an ABI test if you are over 50 with a history of diabetes or smoking. Anyone over 65 should be screened regardless of other risk factors. Additional factors that raise your risk of PAD include high blood pressure, high cholesterol, and a personal history of heart attack or stroke. If you have leg discomfort during exercise that relieves with rest, or if a provider notices weak or absent pulses in your feet, an ABI is typically the first diagnostic step.
Exercise ABI Testing
Some people have leg symptoms that strongly suggest PAD, yet their resting ABI comes back normal. In these cases, a provider may repeat the test immediately after you walk on a treadmill. During exercise, blood vessels in the legs dilate to deliver more oxygen to working muscles. Healthy arteries handle this easily, producing only a small, brief dip in ankle pressure. But when plaque narrows the arteries, the pressure at the ankle drops sharply after exercise because the narrowed vessels can’t keep up with demand. This exaggerated drop confirms PAD that a resting test might miss.
Accuracy and Limitations
The ABI is highly specific, meaning that when it flags PAD, it’s almost always right. Compared to advanced imaging, its specificity ranges from 96% to 100%. However, its sensitivity is lower, between about 7% and 34% in screening populations. That means a normal ABI doesn’t guarantee your arteries are clear. Some people with moderate blockages will still produce a normal score, which is one reason exercise testing or additional imaging may be needed when symptoms are present.
The biggest limitation involves arterial calcification, a process where calcium deposits stiffen the artery walls. This is especially common in people with diabetes and those with reduced kidney function. Stiffened arteries resist compression from the blood pressure cuff, producing an artificially high reading. The result is an ABI above 1.40, or sometimes even a “normal” score that masks real disease underneath. Research has shown that arterial calcification is common even among diabetic patients whose ABI falls at or below 1.40, meaning some cases of PAD go undetected.
When the ABI Isn’t Reliable
For people with stiffened, non-compressible arteries, a toe-brachial index (TBI) is often used instead. This test works the same way but measures pressure in the big toe rather than at the ankle. The smaller arteries in the toes are less prone to calcification, making the reading more accurate. Guidelines recommend TBI testing when the ABI is above 1.40, but some researchers have argued it should be used more broadly in diabetic patients, since calcification can produce falsely normal readings even below that cutoff.