ABI Calculator

Checking Circulation: The Ankle-Brachial Index (ABI)

Peripheral Artery Disease (PAD) occurs when plaque builds up in the arteries of the legs, restricting blood flow. It can cause pain while walking, poor wound healing, and even lead to amputation. The gold standard for screening for this condition is the Ankle-Brachial Index (ABI). Our calculator helps clinicians and patients quickly determine this ratio to assess vascular health.

What is the ABI?

The ABI is a simple ratio that compares the blood pressure in your ankle to the blood pressure in your arm.
- In a healthy person, the pressure in the ankle should be the same as or slightly higher than the arm.
- In a person with blockages, the pressure in the ankle drops significantly.

How to Perform the Test

To get accurate data for this calculator:
1. Patient Position: Lie flat (supine) for 5-10 minutes.
2. Arm Pressure: Measure systolic BP in both arms. Use the higher of the two readings.
3. Ankle Pressure: Measure systolic BP in the ankle (using a Doppler probe on the dorsalis pedis or posterior tibial artery). Use the higher reading of that specific leg.

The Formula

$$ABI = \frac{\text{Highest Ankle Systolic Pressure}}{\text{Highest Arm Systolic Pressure}}$$
Example:
- Right Ankle Pressure: 100 mmHg.
- Highest Arm Pressure: 120 mmHg.
- $ABI = 100 / 120 = 0.83$.

Interpreting the Results

According to the American College of Cardiology (ACC) and American Heart Association (AHA):

> 1.40: Non-Compressible (Abnormal)
Common in patients with diabetes or advanced kidney disease. The arteries are stiff and calcified ("lead pipe" arteries), causing falsely high readings. Toe-Brachial Index (TBI) is recommended instead.

1.00 - 1.40: Normal
No significant blockage.

0.91 - 0.99: Borderline
Some narrowing may be present. Monitor symptoms like claudication (leg pain).

0.41 - 0.90: Mild to Moderate PAD
Significant arterial narrowing. Risk of ulcers and wounds that won't heal increases.

< 0.40: Severe PAD
Critical Limb Ischemia. High risk of rest pain, gangrene, and amputation. Urgent vascular consultation needed.