Peripheral artery disease (PAD) is most commonly diagnosed with a simple, painless test called the ankle-brachial index, or ABI, which compares blood pressure readings in your arms and ankles. The entire process takes about 10 to 15 minutes and requires no needles or dye. Depending on the results, your doctor may stop there or order additional imaging to pinpoint exactly where and how severe any blockages are.
Who Should Be Tested
Not everyone needs PAD screening. The 2024 guidelines from the American College of Cardiology and American Heart Association recommend testing for specific groups based on age and risk factors:
- Age 65 or older: screening is recommended regardless of other risk factors
- Age 50 to 64: if you have diabetes, a smoking history, high blood pressure, high cholesterol, chronic kidney disease, or a family history of PAD
- Under 50: if you have diabetes plus at least one additional risk factor
- Any age: if you already have known artery disease elsewhere, such as coronary artery disease, carotid artery narrowing, or an abdominal aortic aneurysm
Testing younger people without any risk factors has a very low chance of finding PAD, so routine screening in that group isn’t recommended.
The Physical Exam
Before any formal testing, a physical exam can reveal several warning signs. Your doctor will feel the pulses in your feet and legs. Weak or absent pulses are one of the most reliable bedside clues. They’ll also listen with a stethoscope over the arteries in your groin and thighs for a whooshing sound called a bruit, which indicates turbulent blood flow through a narrowed vessel.
Other findings that point toward PAD include skin that feels noticeably cool on one leg compared to the other, slow capillary refill (pressing on a toenail and watching how long it takes for color to return), wounds on the feet or lower legs that won’t heal, and color changes. One classic sign: when you raise your legs, the feet turn pale, and when you lower them back down, they flush a reddish-purple. These findings alone aren’t enough for a definitive diagnosis, but they tell your doctor whether further testing is warranted and how urgently.
The Ankle-Brachial Index (ABI)
The ABI is the standard first-line test for PAD. You’ll lie on your back and rest for 5 to 10 minutes so your blood pressure stabilizes. A technician then wraps a blood pressure cuff around each arm and each ankle, using a small ultrasound device to listen for the pulse as the cuff deflates. The highest ankle pressure on each side is divided by the highest arm pressure, giving a ratio for each leg.
Here’s how those numbers are interpreted:
- 1.0 to 1.4: normal, no significant blockage
- 0.90 to 0.99: borderline, suggesting early or mild disease
- Below 0.90: confirms PAD, with lower numbers indicating more severe narrowing
- Above 1.4: considered abnormally high, usually because the arteries are stiffened by calcium deposits and can’t be compressed normally
The test is painless, takes about 10 minutes, and gives a clear numeric result. It’s also useful for tracking whether PAD is getting worse over time by repeating the measurement at follow-up visits.
When ABI Results Are Unreliable
In people with diabetes or chronic kidney disease, calcium can build up in the artery walls, making them rigid. When this happens, the cuff can’t compress the artery properly, and the ABI reads falsely high, sometimes above 1.4, even when significant blockages exist. This is called medial arterial calcification, and it’s common enough in diabetic patients that ABI alone can’t be trusted.
The workaround is a toe-brachial index (TBI). It works the same way as an ABI but uses a tiny cuff on the big toe. The small arteries in the toes are almost never affected by this type of calcification, so the reading stays accurate. A TBI below 0.6 indicates PAD. Research has confirmed that no patients with a TBI above 0.6 showed arterial insufficiency, making it a reliable alternative when standard ABI values don’t add up.
Exercise Testing for Borderline Cases
Some people have leg symptoms that sound like PAD, such as cramping with walking that stops with rest, but their resting ABI comes back normal. This can happen because blood flow at rest is adequate, but the arteries can’t deliver enough blood when the muscles demand more during activity.
A treadmill exercise test solves this. You walk on a treadmill, usually at a standardized speed and incline, and the ABI is measured again immediately afterward. A drop in the ankle-brachial index of more than 20% after exercise confirms PAD. An older criterion using an absolute ankle pressure drop greater than 30 mmHg is less sensitive and catches only about 28% of cases, compared to roughly 57% for the 20% drop threshold. The exercise test is especially valuable for active people whose symptoms only appear during physical effort.
Duplex Ultrasound
Once PAD is confirmed, your doctor may want to know exactly where the blockages are and how severe they’ve become. Duplex ultrasound combines a standard ultrasound image with measurements of blood flow speed through the arteries. It’s noninvasive, uses no radiation, and can map the arteries from your abdomen down to your ankles.
The test works by measuring how fast blood moves through different segments. In a healthy artery, blood flow has a characteristic three-phase pattern: a strong forward push, a brief reversal, then a small forward wave. As PAD progresses, the artery loses its elasticity, and this pattern simplifies to two phases, then eventually a single sluggish wave, which signals severe disease or blockage.
Technicians also calculate a velocity ratio by comparing the speed of blood at a narrowed point to the speed just upstream. A ratio of 2 to 4 indicates 50% to 75% narrowing. A ratio above 4 means more than 75% of the artery is blocked. Speeds above 300 cm/s at a narrowed site with a ratio above 3.5 classify the stenosis as severe. If an artery is completely blocked, no flow appears on the ultrasound at that point.
CT and MR Angiography
When surgery or a catheter-based procedure is being considered, your doctor needs a detailed roadmap of the arteries. CT angiography (CTA) and MR angiography (MRA) both provide this, using contrast dye to create detailed images of the blood vessels.
CTA uses X-rays and is fast, widely available, and highly accurate. MRA uses magnetic fields instead, avoiding radiation but taking longer. Both perform well in the larger arteries of the pelvis and thigh, with accuracy around 90% to 94% for classifying disease in those regions. CTA has an edge when it comes to the smaller arteries below the knee, where its accuracy reaches about 96% compared to 90% for MRA. CTA is also slightly better at evaluating the overall state of the smaller “runoff” arteries in the lower leg, which matters when planning bypass surgery or stenting.
MRA is often preferred for people with kidney problems, since certain MRA techniques can reduce the amount of contrast dye needed. CTA, on the other hand, is usually the go-to for patients with metal implants or pacemakers that make MRI unsafe.
Catheter-Based Angiography
Traditional angiography, where a thin catheter is threaded into the artery and dye is injected while X-ray images are taken in real time, is rarely used purely for diagnosis anymore. The noninvasive options have largely replaced it for that purpose. Today, catheter-based angiography is typically reserved for situations where treatment is planned during the same procedure. A doctor can thread a catheter into the blocked artery, confirm the exact location and severity of the narrowing on a live X-ray image, and then immediately open it with a balloon or stent.
Because it’s invasive and carries small risks like bleeding at the catheter insertion site, it’s only used when the diagnostic information will directly guide a procedure that’s already being performed.
How These Tests Fit Together
For most people, the diagnostic path is straightforward. A physical exam and ABI are enough to confirm or rule out PAD. If the ABI is borderline or normal but symptoms persist, exercise testing clarifies the picture. If the ABI is unreliable because of calcified arteries, the toe-brachial index steps in. Once PAD is confirmed and treatment decisions need to be made, duplex ultrasound, CT angiography, or MR angiography provides the anatomical detail. Each test builds on the one before it, and most people will only need the first one or two steps to get a clear answer.