Ankle Brachial Index (ABI)

Calculate ABI ratio.

Result:

The Ankle-Brachial Index (ABI): Screening for Peripheral Artery Disease

Cardiovascular disease is the number one killer globally, but many people only think about the heart. However, the exact same plaque buildup (atherosclerosis) that causes heart attacks can occur in the arteries of your legs. This is known as Peripheral Artery Disease (PAD). The Ankle-Brachial Index (ABI Calculator) is the simplest, non-invasive way to diagnose this condition before it leads to severe complications like amputation or stroke.

What is the ABI?

Gravity makes blood pressure naturally higher in the legs than the arms when standing. However, when lying flat, the pressure should be roughly equal.
The ABI is a ratio comparing the blood pressure in your ankle to the blood pressure in your arm.

The Logic: To get to your ankle, blood must travel through the aorta, into the iliac arteries, down the femoral arteries, and into the tibial arteries. If there is a blockage (plaque) anywhere along that long highway, the pressure arriving at the ankle will be lower than expected.

How to Measure Properly

You cannot use a standard automated cuff for an accurate ABI. You need a Handheld Doppler probe.

1. Preparation:
Have the patient lie supine (flat on their back) for 10 minutes to normalize pressures.

2. Arm Pressure (Brachial):
Measure systolic pressure in BOTH arms. Use the Higher of the two values.

3. Ankle Pressure (Dorsalis Pedis / Posterior Tibial):
Measure systolic pressure in the ankle. Again, if measuring both arteries, take the higher value.

4. The Formula:
ABI = Ankle Systolic Pressure / Arm Systolic Pressure

Interpreting the Results

Current clinical guidelines categorize ABI ratios as follows:

> 1.40: Non-Compressible (Calcified)
This is typical in patients with long-standing diabetes or advanced kidney disease. The arteries are so stiff with calcium that the blood pressure cuff cannot squeeze them shut. The result is artificially high and unreliable. A Toe-Brachial Index (TBI) is needed instead.

1.00 â€“ 1.40: Normal
Blood flow is unobstructed.

0.91 â€“ 0.99: Borderline
Start reducing risk factors (exercise, smoking cessation).

0.41 â€“ 0.90: Mild to Moderate PAD
The patient may experience "Claudication"â€”pain in the calves when walking that stops when resting. This indicates that blood flow is sufficient for rest but insufficient for exercise.

â‰¤ 0.40: Severe PAD
This is "Critical Limb Ischemia." The patient likely has pain even when resting (rest pain) and is at high risk for non-healing ulcers and gangrene.

Risk Factors for PAD

Who should get tested?

Smokers: Smoking is the #1 risk factor for PAD.
Diabetics: High blood sugar damages blood vessel walls.
Age 50+: Especially if you have a history of high blood pressure or high cholesterol.
African Americans: Statistically have a higher prevalence of PAD.

Why Early Diagnosis Matters

PAD is a "canary in the coal mine." If you have plaque in your legs, you almost certainly have plaque in your heart (coronary arteries) and brain (carotid arteries). Diagnosing PAD with a simple ABI test gives doctors a chance to treat the systemic atherosclerosis aggressively with statins, antiplatelets (aspirin), and lifestyle changes, preventing future heart attacks and strokes.

Disclaimer: This calculator is for educational purposes. If you suspect you have PAD or experience leg pain while walking, see a vascular specialist immediately.