Peripheral artery disease (PAD) is diagnosed through a combination of physical examination, blood pressure measurements in your legs, and, when needed, imaging tests that map the arteries. The first-line diagnostic tool, recommended by the American Heart Association and American College of Cardiology, is the resting ankle-brachial index (ABI), a quick, painless test that can be done in a regular office visit.
The Physical Exam
Before any formal testing, your doctor will check the pulses in your legs and feet by pressing on specific arteries: the femoral artery in your groin, the popliteal artery behind your knee, the posterior tibial artery near your inner ankle, and the dorsalis pedis artery on top of your foot. Each pulse is graded on a 0 to 4 scale. A grade of 3 is normal and easy to feel, while a 1 means barely detectable and a 0 means no pulse at all. Weak or absent pulses in your lower extremities are a strong early signal of blocked arteries.
Your doctor will also look for other physical signs: cool skin on the legs or feet, slow-healing wounds, changes in skin color, and hair loss below the knee. These findings alone don’t confirm a diagnosis, but they help determine which tests to order next.
The Ankle-Brachial Index
The ABI is the cornerstone of PAD diagnosis. A technician places blood pressure cuffs on both of your arms and both ankles, then uses a handheld ultrasound probe to listen to blood flow. The systolic (top number) blood pressure at your ankle is divided by the systolic pressure in your arm. Because your legs are farther from the heart, the pressure there is normally equal to or slightly higher than in your arms.
The results break down into clear ranges:
- 1.0 to 1.3: Normal
- 0.7 to 0.9: Mild PAD
- 0.4 to 0.7: Moderate PAD
- Below 0.4: Severe PAD
The whole test takes about 15 minutes, involves no needles, and requires no special preparation. It’s often the only test needed to confirm or rule out PAD in most people.
When ABI Results Are Unreliable
In people with diabetes or chronic kidney disease, calcium deposits can stiffen the artery walls in the lower leg, making the arteries difficult to compress. This produces an ABI above 1.3, which looks “super normal” but is actually a false reading. The arteries may still be significantly narrowed on the inside even though the walls won’t collapse under a blood pressure cuff.
For these patients, a toe-brachial index (TBI) is the better option. The smaller arteries in the toes are less prone to calcification, so the reading is more accurate. A TBI below 0.6 suggests PAD. The test works just like the ABI but uses a tiny cuff around your big toe instead of your ankle.
Exercise Testing for Borderline Results
Some people have leg pain with walking but a normal resting ABI. That’s because mild blockages may not restrict blood flow enough to show up at rest but become significant when the muscles demand more oxygen during movement. In these cases, your doctor may order a treadmill exercise test.
The standard protocol uses a treadmill set to a 10% incline at about 3.2 km/h (roughly 2 mph), a comfortable walking pace. You walk for up to 20 minutes or until symptoms stop you. Immediately after, ABI measurements are taken again. A drop in ankle pressure of 30 mmHg or more from your resting value, or a post-exercise ABI decrease greater than 20%, confirms PAD. This test is particularly useful for catching early-stage disease that a resting ABI would miss entirely.
Duplex Ultrasound
Once PAD is confirmed, your doctor may want to know exactly where the blockages are and how severe they’ve become. A duplex ultrasound combines a standard ultrasound image with Doppler technology that measures the speed of blood flow through your arteries. It’s painless, uses no radiation, and typically takes 30 to 60 minutes depending on how many arteries need to be examined.
The technician looks at how fast blood moves through narrowed sections compared to healthy sections nearby. When blood squeezes through a tight spot, it speeds up, much like water through a pinched garden hose. A speed ratio of 2 to 4 between the narrowed and normal segments indicates 50% to 75% blockage. A ratio above 4 means more than 75% of the artery is blocked.
The shape of the blood flow waveform also tells a story. Healthy arteries produce a crisp, three-phase wave pattern. Moderate disease flattens this into a two-phase pattern, and severe disease reduces it to a single sluggish wave. These waveform changes help pinpoint disease even in areas where measuring speed ratios is difficult.
CT and MR Angiography
When your doctor needs a detailed roadmap of your entire arterial system, typically before planning a procedure to open or bypass a blockage, CT angiography (CTA) or MR angiography (MRA) provides it. Both techniques produce detailed three-dimensional images of your arteries and detect significant blockages with 90% to 100% accuracy.
CTA uses X-rays and requires an injection of iodine-based contrast dye. The scan itself is fast, usually under 10 minutes, though preparation and IV placement add time. MRA uses magnetic fields instead of radiation and typically uses a gadolinium-based contrast agent, though some newer protocols can skip contrast altogether.
The choice between the two often comes down to your kidney function. The contrast dye used in both CTA and MRA can stress the kidneys. For people with moderately reduced kidney function, the risk of contrast-related kidney injury runs around 8% to 13%, rising to 27% in people with severely impaired kidneys. If your kidney function is significantly reduced, your doctor may choose contrast-free MRA or rely on ultrasound instead.
Catheter-Based Angiography
Traditional angiography, where a thin catheter is threaded through an artery (usually starting at the groin) and contrast dye is injected while X-ray images are taken in real time, is the most detailed way to visualize arterial blockages. It’s considered the gold standard for image quality.
However, because it’s invasive and carries a small risk of complications, it’s generally reserved for situations where noninvasive imaging results are inconclusive or when a treatment procedure is planned at the same time. If a blockage is found during the angiogram, your doctor can often treat it in the same session by inflating a tiny balloon or placing a stent to hold the artery open.
What the Diagnostic Process Looks Like in Practice
For most people, diagnosis follows a predictable path. It starts with a conversation about your symptoms, especially leg pain or cramping during walking that goes away with rest. A physical exam and resting ABI come next. If the ABI is abnormal, that’s often enough to confirm PAD and start treatment. If symptoms are suggestive but the ABI is normal, an exercise treadmill test can unmask hidden disease. If diabetes makes ABI unreliable, a toe-brachial index replaces it.
Imaging enters the picture only when your doctor needs to locate and measure specific blockages, usually because a procedure is being considered. You may go through duplex ultrasound first, then CTA or MRA if more detail is needed. Catheter angiography comes last, and only when less invasive options haven’t provided enough information or when treatment can happen simultaneously.