Peripheral Artery Disease and the Ankle-Brachial Index

The short answer#

Peripheral artery disease (PAD) is narrowing of the arteries that carry blood to the legs, almost always from atherosclerosis, the same plaque process behind heart attack and stroke. The classic symptom is claudication: a cramp, ache, or tightness in the calf, thigh, or buttock that comes on with walking and eases within a few minutes of standing still. Most people, though, have no classic symptom at all. The anchor test is the ankle-brachial index (ABI), a painless comparison of blood pressure at the ankle and the arm. An ABI of 0.90 or lower confirms PAD.

Key points#

• PAD is atherosclerosis in the leg arteries. It affects more than 10 million adults in the United States and over 200 million people worldwide, and it becomes common with age (roughly 1 in 5 people past 80).
• Cramping calf pain with walking (claudication) is the textbook sign, but only about 10% to 30% of people with PAD have it. Most are silent or have atypical leg symptoms, which is why the condition is so often missed.
• The resting ABI, the ratio of ankle to arm systolic pressure, is the first-line diagnostic test. An ABI of 0.90 or lower establishes PAD (2024 ACC/AHA guideline, a Class 1 recommendation).
• An ABI above 1.40 signals stiff, noncompressible arteries (common with diabetes or kidney disease). A toe-brachial index is used instead.
• PAD is a marker of body-wide atherosclerosis. A low ABI roughly doubles the risk of heart attack, stroke, and cardiovascular death, so a diagnosis should prompt full risk-factor treatment.
• Structured, supervised walking programs are first-line therapy and improve walking distance more than advice alone. Stopping smoking, high-intensity statins, and antiplatelet therapy lower the risk of major events.
• A suddenly cold, pale, painful, or numb leg, foot pain at rest, or a non-healing foot wound are red flags that need urgent care.

What are the symptoms of peripheral artery disease?#

Here is the trap that makes PAD easy to overlook: most people who have it do not have the textbook complaint. Across large populations, only a minority (roughly 10% to 30%) report classic intermittent claudication. Another large group has atypical leg symptoms, and many have no leg symptoms at all. That does not mean these arteries are harmless. People labeled "asymptomatic" have often trimmed their own activity without realizing it, walking slower or less to avoid discomfort, and they carry the same body-wide cardiovascular risk.

When symptoms do appear, they tend to follow a pattern worth learning:

• Muscle cramp, ache, fatigue, or tightness, usually in the calf, sometimes the thigh or buttock, brought on by walking.
• Pain that is reproducible: it appears after a fairly consistent distance and is worse walking fast or uphill.
• Relief within a few minutes of simply standing still, without needing to sit or change position.

More advanced disease produces symptoms at rest. Pain in the forefoot or toes at night that improves when the leg hangs over the side of the bed, cool or shiny skin, hair loss over the shins, slow-healing scrapes, or a wound that will not close all point to reduced blood flow. Those features move the picture toward the severe end of the spectrum, chronic limb-threatening ischemia, which is covered in its own guide.

Why do my legs hurt when I walk, and is it always PAD?#

Leg pain with walking has several causes, and telling them apart guides testing. True vascular claudication comes from muscle that outruns its blood supply, so it is tied to effort and relieved by rest. Several common mimics behave differently.

Pseudoclaudication from spinal stenosis is the most frequent look-alike. The distinguishing question is what makes it stop: PAD eases when you halt, while spinal stenosis eases when you sit or bend forward, because that posture opens the spinal canal. When the story is not clean, or when leg pulses feel diminished, an objective test settles it.

What is an ankle-brachial index?#

The ankle-brachial index is the workhorse of PAD diagnosis: quick, inexpensive, non-invasive, and validated. A clinician measures systolic blood pressure in both arms and at both ankles (using a Doppler probe), then divides the higher ankle pressure in each leg by the higher of the two arm pressures. In healthy arteries the ankle pressure is at least as high as the arm, so the ratio sits near or slightly above 1.0. When plaque narrows the leg arteries, ankle pressure falls and the ratio drops.

The 2024 ACC/AHA multisociety guideline recommends a resting ABI to establish the diagnosis in anyone with history or physical findings that suggest PAD (a Class 1 recommendation). It is also reasonable to test at-risk people without symptoms, for example those who smoke or have smoked, have diabetes, have known atherosclerosis elsewhere, or are older than 65.

Standard thresholds from the American Heart Association measurement statement:

Two caveats matter. First, a resting ABI can be normal even when someone has real claudication; adding an exercise (post-walk) ABI can unmask a pressure drop that only shows under demand. Second, an ABI above 1.40 usually means the vessel walls are too stiff to compress, often with long-standing diabetes or kidney disease. That value cannot be trusted to rule out PAD, so a toe-brachial index (toe arteries calcify less) or imaging is used instead. Note that the US Preventive Services Task Force separately concluded there is insufficient evidence to screen truly asymptomatic adults purely to estimate general cardiovascular risk; that is a different question from testing someone with symptoms or clear risk factors, where the ABI is the standard diagnostic step.

Why does PAD matter beyond the legs?#

A low ABI is not only about walking distance. Because PAD reflects atherosclerosis throughout the body, people who have it commonly have plaque in the coronary and carotid arteries too. A reduced ABI roughly doubles the risk of heart attack, stroke, and cardiovascular death, independent of symptoms and of other risk factors. In other words, the leg finding is a window onto whole-body arterial health.

That reframes the goal. Finding PAD is a prompt to treat global cardiovascular risk aggressively, not just to address the legs. This is where formal risk estimation and prevention strategy come in, and the guides on understanding cardiovascular risk scores and on cardiometabolic prevention (what the evidence actually supports) connect directly to this diagnosis.

What helps if you have PAD?#

Management works on two fronts at once: improving walking and lowering the risk of heart attack and stroke.

For symptoms, structured exercise is first-line. Supervised exercise therapy, or a structured community-based program, earns a Class 1, Level A recommendation to improve walking performance and quality of life. The evidence is concrete: a Cochrane review found that supervised programs increased treadmill walking distance by roughly 120 to 210 meters more at three months than home-based exercise or walking advice alone. The core is walking to moderate claudication discomfort, resting, and repeating, several times a week.

For risk, the levers are well established:

• Stopping smoking is the single most important modifiable step. It slows disease progression and cuts cardiovascular and amputation risk.
• High-intensity statin therapy, aiming for at least a 50% reduction in LDL cholesterol, carries a Class 1, Level A recommendation.
• Single antiplatelet therapy (aspirin or clopidogrel) is recommended for symptomatic PAD to reduce major cardiovascular events. Low-dose rivaroxaban added to aspirin is an option in selected patients under specialist guidance.
• Controlling blood pressure and, where relevant, diabetes rounds out the medical plan. Careful daily foot care matters, especially with diabetes, to catch small wounds early.

Cilostazol can improve walking distance for some people with lifestyle-limiting claudication. Revascularization (angioplasty, stenting, or surgery) is reserved for symptoms that stay limiting despite good medical therapy and exercise, or for the limb-threatening end of the spectrum. Anyone with PAD also fits within the broader picture of heart, lung, and acute care, since the same arterial disease drives events elsewhere.

When to seek care#

Some situations need prompt or emergency attention:

• A leg or foot that suddenly becomes cold, pale or bluish, painful, numb, or weak. Sudden loss of blood flow (acute limb ischemia) is an emergency; call emergency services.
• Pain in the foot or toes at rest, or pain at night that eases only when you hang the leg down.
• A sore, ulcer, or wound on the foot or leg that is not healing, or any blackened tissue.
• Signs of infection in a foot wound (spreading redness, warmth, drainage, fever), particularly with diabetes.
• New or worsening claudication that is limiting daily activity, so testing and treatment can start.

If you have leg pain with walking or risk factors for arterial disease, talk with a clinician about whether an ankle-brachial index is right for you.