Ankle-Brachial Index (ABI)

The ankle-brachial index, or ABI, is a simple comparison: the blood pressure measured at your ankle divided by the blood pressure measured in your arm. In healthy arteries those pressures are similar. When the arteries carrying blood to the legs are narrowed by plaque, the pressure at the ankle falls behind — and the ratio quantifies how far.

It takes about 15 minutes, uses ordinary blood pressure cuffs and a small Doppler probe, and involves no needles, dye or radiation.

• 1.00 – 1.40 — normal
• 0.91 – 0.99 — borderline
• 0.90 or below — consistent with peripheral artery disease; the lower the value, the more severe the blockage
• Above 1.40 — the vessels are too stiff to compress, common in long-standing diabetes or kidney disease, and means the ABI is unreliable and a different test is needed

Peripheral artery disease is a marker of atherosclerosis throughout the body. Someone with a low ABI has a meaningfully higher risk of heart attack and stroke even if their legs never trouble them, so an abnormal result changes how aggressively cholesterol, blood pressure, diabetes and smoking are managed — not just how the legs are treated.

• Leg pain, aching or cramping brought on by walking and relieved by rest (claudication)
• Leg or foot wounds that are slow to heal
• Coldness, color change, or hair loss on the lower legs and feet
• Diabetes, a smoking history, or known coronary or carotid disease, as screening
• Following a known blockage or a prior revascularization over time

You lie flat and rest quietly for several minutes first, since a recent walk or a rush into the office will skew the reading. Cuffs are placed on both arms and both ankles and inflated one at a time while a Doppler probe listens over the artery. It feels like any blood pressure check — firm squeezing that releases after a few seconds.

A treadmill ABI is sometimes added: pressures are taken again immediately after walking, because narrowing that is mild at rest can become obvious under the demand of exercise. If your resting study is normal but your symptoms are classic, this is often the next step.

An abnormal ABI usually leads to a vascular ultrasound to locate the blockage precisely, along with a review of the risk factors driving it. Most peripheral artery disease is managed without surgery — structured walking, cholesterol and blood pressure control, diabetes management, and stopping smoking are the foundation of treatment, and procedures are reserved for symptoms that limit daily life or for wounds that will not heal.