Peripheral artery disease (PAD) is most commonly diagnosed with a simple, painless test called the ankle-brachial index, or ABI. This test compares blood pressure readings at your ankle to those in your arm and can be done in a doctor’s office in about 10 minutes. But depending on your symptoms, risk factors, and initial results, your doctor may use several other tools to confirm the diagnosis and pinpoint where arteries have narrowed.
The Physical Exam
Diagnosis typically starts with a hands-on examination. Your doctor will check the pulses in your legs and feet at four key locations: the femoral artery (in the groin), the popliteal artery (behind the knee), and two arteries at the ankle and top of the foot. Pulses are graded on a 0-to-3 scale, where 0 means absent and 2 is normal. Weak or missing pulses are one of the strongest clues.
Your doctor will also listen over the femoral artery with a stethoscope for a “bruit,” a whooshing sound caused by turbulent blood flow through a narrowed vessel. If a bruit is heard, the stethoscope can be moved up toward the pelvis and belly button to help locate where the blockage sits. The combination of absent ankle pulses and a femoral bruit is particularly telling.
Beyond pulses and sounds, the appearance of your legs and feet matters. Signs that suggest restricted blood flow include cool skin, slow capillary refill (press a toenail and see how long it takes to turn pink again), wounds that won’t heal, and dry ulcers at the toes or ball of the foot. In more advanced disease, elevating the feet causes them to turn pale, while dangling them back down produces a deep redness called dependent rubor. Asymmetric hair loss on the legs can also be a clue, though on its own it isn’t reliable.
The Ankle-Brachial Index
The ABI is the standard first-line test for PAD. A blood pressure cuff is placed on your arm and then on your ankle, and a small ultrasound probe (Doppler) picks up the pulse at each site. The ankle pressure is divided by the arm pressure to produce a ratio.
Here’s how the numbers break down:
- 1.00 to 1.40: Normal blood flow
- 0.91 to 0.99: Borderline, may warrant further testing
- 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 properly, making the result unreliable
A meta-analysis pooling data from four studies found that an ABI of 0.90 or below correctly identifies PAD about 75% of the time (sensitivity) and correctly rules it out about 86% of the time (specificity). Those numbers make it a useful screening tool, but not a perfect one. Some people with real blockages will have a normal resting ABI, especially if their disease is mild or their arteries are calcified.
When Resting ABI Isn’t Enough
If your symptoms sound like PAD (cramping leg pain when you walk that stops when you rest) but your resting ABI comes back normal, your doctor may repeat the test after exercise. You’ll walk on a treadmill for a few minutes, then have your ankle pressure measured again right away. A drop of more than 15% in the ABI value, or a fall of 20 mmHg or more in ankle pressure, points toward PAD that only shows up when your muscles demand more blood. Exercise testing essentially unmasks blockages that don’t cause trouble at rest.
Toe-Brachial Index for Diabetes and Kidney Disease
People with diabetes, chronic kidney disease, or advanced age often develop calcium deposits in their artery walls. This stiffening prevents the arteries at the ankle from compressing normally under a blood pressure cuff, which inflates the ABI reading and can hide real disease. A standard ABI above 0.9, including values that look perfectly “normal,” frequently misses PAD in these groups.
The toe-brachial index (TBI) solves this problem. It works the same way as the ABI, but uses a tiny cuff on the big toe instead of the ankle. The small arteries in the toes are largely spared from calcification. A TBI below 0.6 indicates PAD. Research comparing both tests against CT angiography in people with type 2 diabetes found that TBI had substantially better agreement with imaging results than ABI did. For anyone with diabetes and a normal-looking ABI, the TBI is the more trustworthy bedside test.
Imaging Tests
Once PAD is confirmed, imaging may be needed to map exactly where and how severe the blockages are, particularly if a procedure to restore blood flow is being considered.
Duplex Ultrasound
This combines standard ultrasound with Doppler technology to produce images of blood flowing through your arteries. It’s noninvasive, uses no radiation, and is the least expensive imaging option. Its sensitivity for detecting significant narrowing (more than 50% blockage) ranges from 80 to 98%, with specificity from 89 to 99%. It works well for evaluating specific segments of the leg, and studies have found it comparable to invasive angiography for surgical planning.
CT Angiography (CTA)
A CT scan taken after contrast dye is injected into a vein produces detailed three-dimensional maps of your arteries. Sensitivity ranges from 89 to 99%, and specificity from 83 to 97%. CTA is fast and widely available, though it does involve radiation exposure and the contrast dye can be a concern for people with kidney problems.
Magnetic Resonance Angiography (MRA)
Contrast-enhanced MRA has the highest overall diagnostic accuracy of the three, with sensitivity from 92 to 99.5% and specificity from 64 to 99%. It uses no radiation. The tradeoffs are longer scan times, higher cost, and the fact that it can’t be used in people with certain metal implants or pacemakers.
Catheter-Based Angiography
This invasive test threads a thin catheter into an artery and injects dye directly to visualize blockages in real time on X-ray. It was once the gold standard for diagnosis, but today most centers reserve it for situations where a treatment procedure (like placing a stent or inflating a balloon) is planned at the same time. For purely diagnostic purposes, the noninvasive options above have largely replaced it.
Conditions That Mimic PAD
Leg pain with walking isn’t always caused by blocked arteries. Spinal stenosis, a narrowing of the spinal canal in the lower back, can produce very similar cramping in the legs. The key difference is that spinal stenosis pain often improves when you lean forward or sit down, while PAD pain eases simply by standing still. Deep vein thrombosis (a blood clot in a leg vein) causes swelling, warmth, and tenderness rather than the exercise-related cramping of PAD. Nerve damage from diabetes, arthritis in the hip or knee, and chronic compartment syndrome can all overlap with PAD symptoms as well. The ABI and imaging tests described above are what separate arterial disease from these look-alikes.