Testing for peripheral artery disease (PAD) starts with a simple, painless blood pressure comparison between your arms and ankles called the ankle-brachial index, or ABI. This 15-to-30-minute office test is the standard first step recommended by the American College of Cardiology and American Heart Association. If results are abnormal or inconclusive, your doctor may move on to imaging or exercise-based tests to pinpoint where and how severe the blockages are.
The Physical Exam: What Your Doctor Checks First
Before any formal testing, a vascular exam gives your doctor early clues. They’ll feel for pulses at several points along your legs: the groin, behind the knee, the top of the foot, and the inner ankle. Weak or absent pulses at any of these sites suggest reduced blood flow. They’ll also listen over the femoral artery in your groin with a stethoscope, checking for a “bruit,” a whooshing sound caused by turbulent blood squeezing through a narrowed artery.
Other signs they look for include skin that feels cool to the touch, slow capillary refill (pressing a toenail and watching how quickly color returns), wounds on the feet or legs that won’t heal, and color changes. One classic finding is called “dependent rubor”: your feet turn pale when elevated above heart level, then shift to a deep red when you hang them down. Any of these findings prompts the next step.
The Ankle-Brachial Index (ABI)
The ABI is the cornerstone screening test for PAD. You’ll lie flat on an exam table for 15 to 30 minutes to let your blood pressure settle. A technician then wraps a standard blood pressure cuff around your upper arm and inflates it while using a small handheld Doppler device to listen to the artery at your elbow. They repeat this on the other arm, then measure blood pressure at both ankles, placing the cuff just above the ankle bone. The American Heart Association recommends a specific order: first arm, same-side ankle, opposite ankle, then opposite arm.
The result is a simple ratio. Your highest ankle pressure is divided by your highest arm pressure. Here’s what the numbers mean:
- 1.00 to 1.40: Normal
- 0.91 to 0.99: Borderline
- 0.41 to 0.90: Mild to moderate PAD
- 0.00 to 0.40: Severe PAD
- Above 1.40: Arteries are too stiff to compress reliably (common in diabetes)
No needles, no contrast dye, no special preparation beyond resting beforehand. The entire test takes about 15 to 30 minutes and can be done in a regular office visit.
When the ABI Isn’t Enough: The Toe-Brachial Index
People with diabetes or chronic kidney disease often have calcium deposits that stiffen the walls of leg arteries, making them resist compression. This produces a falsely high ABI, sometimes above 1.40, even when real blockages exist. In these cases, doctors use the toe-brachial index (TBI) instead. A tiny pressure cuff is placed around the big toe, where arteries are generally spared from this type of calcification. A TBI below 0.6 indicates PAD. Research has confirmed that no patients with a TBI above 0.6 showed arterial insufficiency on follow-up angiography, making it a reliable alternative when the standard ABI gives misleading results.
Exercise Testing for Borderline Results
A resting ABI can miss mild PAD because blockages that don’t limit blood flow at rest may become a problem during activity. If your resting ABI is borderline or your symptoms point to PAD despite a normal number, your doctor may order an exercise ABI. You walk on a treadmill, and your ankle pressures are rechecked immediately afterward. A drop in ankle pressure after walking confirms the diagnosis.
Two common treadmill protocols exist. The constant-load test has you walk at 2 mph on a 10% to 12% incline. The graded test starts flat at 2 mph and increases the incline by 2% every two minutes until leg pain forces you to stop. The graded approach is particularly useful for mild PAD because it gradually pushes you to a point where the diseased arteries can’t keep up, giving the doctor a clearer picture of your functional limits.
Duplex Ultrasound: Mapping the Blockages
Once PAD is confirmed, your doctor often needs to know exactly where the narrowing is and how severe it has become. Duplex ultrasound combines a standard imaging scan with Doppler technology that tracks the speed and direction of blood flow through your arteries. It’s painless, uses no radiation, and requires no contrast dye.
The test works on a straightforward principle: when blood squeezes through a narrowed section of artery, it speeds up, the same way water shoots faster through a pinched garden hose. The technician measures peak blood flow velocity at the narrowed spot and compares it to a normal section nearby. The greater the velocity jump, the tighter the blockage. On the screen, areas of turbulence show up as color changes or a whitening effect where blood flow becomes chaotic instead of smooth. The technician can also hear the difference. A healthy artery produces a clean, rhythmic sound, while a narrowed one creates a high-pitched, thumping signal.
CT and MR Angiography
When your doctor needs a detailed roadmap of your arteries, particularly before planning a procedure, they may order a CT angiography (CTA) or magnetic resonance angiography (MRA). Both create high-resolution images of the entire arterial tree from the abdomen down to the feet, and both detect blockages with 90% to 100% sensitivity and specificity.
CTA uses X-rays and an iodine-based contrast dye injected into a vein. It’s fast and widely available, but it does involve radiation exposure and may be less clear in people with heavy calcification or metal implants. If you’ve had allergic reactions to contrast dye before, you may need medication starting 24 hours before the scan, or your doctor may choose a different test entirely.
MRA uses magnetic fields instead of radiation, with a gadolinium-based contrast agent. It avoids the radiation concern but takes longer and can also lose image quality around metal implants or stents. Neither test is inherently better than the other for accuracy. The choice typically depends on your specific health situation, whether you have kidney problems, metal implants, or contrast allergies.
Catheter Angiography
This is the most detailed test available, but it’s also the most invasive. A thin catheter is threaded through an artery, typically starting at the groin, and contrast dye is injected directly while X-ray images are taken in real time. It produces the sharpest view of plaque buildup and narrowing.
Catheter angiography is generally reserved for situations where treatment is planned at the same time. If a significant blockage is found during the procedure, the doctor can often open it with a balloon or place a stent right then, turning a diagnostic test into a treatment in the same session. Because it carries more risk than non-invasive options, including reactions to the iodine contrast and potential complications at the catheter insertion site, it’s not used as a first-line screening tool.
How These Tests Fit Together
The diagnostic pathway follows a logical sequence. A physical exam and resting ABI come first. If the ABI is borderline, an exercise treadmill test can unmask hidden disease. If the ABI reads abnormally high due to stiff arteries, the toe-brachial index steps in. Once PAD is confirmed, duplex ultrasound locates the blockages without any contrast or radiation. CT or MR angiography provides a comprehensive map when a procedure is being considered. Catheter angiography is the final step, reserved for cases where intervention is likely during the same appointment.
Most people only need the first one or two tests. The ABI alone correctly identifies PAD in the large majority of cases, and it can be done in a routine office visit with nothing more than a blood pressure cuff and a Doppler probe.