The Ankle-Brachial Index (ABI) is a non-invasive medical test used to screen for Peripheral Artery Disease (PAD). By comparing the systolic blood pressure in your ankles to the systolic blood pressure in your arms, clinicians can identify blockages or narrowing in the arteries that supply blood to your legs.
How the ABI is Calculated
The calculation is a ratio derived from the highest systolic blood pressure measured at the ankle divided by the highest systolic blood pressure measured in the arms. To perform this calculation accurately, you need measurements from both the posterior tibial or dorsalis pedis artery in the ankle and the brachial artery in the arm.
The Formula: ABI (Leg) = Highest Systolic Ankle Pressure (Leg) / Highest Systolic Arm Pressure (Both Arms)
ABI Results Interpretation
ABI Range
Interpretation
1.00 – 1.40
Normal (No PAD)
0.91 – 0.99
Borderline PAD
0.71 – 0.90
Mild PAD
0.41 – 0.70
Moderate PAD
≤ 0.40
Severe PAD
> 1.40
Non-compressible / Calcified Vessels
Example Calculation
Suppose a patient has the following systolic blood pressure readings:
Right Arm: 120 mmHg
Left Arm: 124 mmHg
Right Ankle: 110 mmHg
Left Ankle: 130 mmHg
First, identify the highest arm pressure, which is 124 mmHg. Next, divide each ankle pressure by this value:
Right ABI: 110 / 124 = 0.89 (Mild PAD)
Left ABI: 130 / 124 = 1.05 (Normal)
Why is the ABI Important?
An ABI test is crucial because Peripheral Artery Disease is often a "silent" condition. Many people with PAD experience no symptoms, yet they are at a higher risk for heart attacks, strokes, and leg amputations. Identifying a low ABI early allows for lifestyle changes and medical interventions that can significantly improve cardiovascular health and mobility.
function calculateABI() {
var rArm = parseFloat(document.getElementById('rightArm').value);
var lArm = parseFloat(document.getElementById('leftArm').value);
var rAnkle = parseFloat(document.getElementById('rightAnkle').value);
var lAnkle = parseFloat(document.getElementById('leftAnkle').value);
var resultArea = document.getElementById('abiResultArea');
var rightResDiv = document.getElementById('rightResult');
var leftResDiv = document.getElementById('leftResult');
var interpDiv = document.getElementById('abiInterpretation');
if (isNaN(rArm) || isNaN(lArm) || isNaN(rAnkle) || isNaN(lAnkle)) {
alert("Please enter valid numeric values for all fields.");
return;
}
if (rArm <= 0 || lArm 1.4 || abiLeft > 1.4) {
interpretation = "Result Suggests Non-compressible / Calcified Vessels (> 1.40)";
bgColor = "#f39c12";
} else if (worstABI >= 1.0) {
interpretation = "Normal (No PAD)";
bgColor = "#27ae60";
} else if (worstABI >= 0.91) {
interpretation = "Borderline PAD";
bgColor = "#f1c40f";
textColor = "#000";
} else if (worstABI >= 0.71) {
interpretation = "Mild PAD";
bgColor = "#e67e22";
} else if (worstABI >= 0.41) {
interpretation = "Moderate PAD";
bgColor = "#d35400";
} else {
interpretation = "Severe PAD";
bgColor = "#c0392b";
}
interpDiv.innerHTML = interpretation;
interpDiv.style.backgroundColor = bgColor;
interpDiv.style.color = textColor;
}