The Ankle Brachial Index (ABI) is a simple, non-invasive diagnostic test used to assess circulation to the lower legs. It compares the blood pressure in the ankles to the blood pressure in the arms. This ratio is a crucial indicator of peripheral artery disease (PAD), a condition where the arteries that supply blood to the legs and feet become narrowed or blocked.
How the ABI is Calculated
The calculation of the Ankle Brachial Index is straightforward:
ABI = (Highest Systolic Blood Pressure in the Ankle) / (Highest Systolic Blood Pressure in the Arm)
To perform the test, two blood pressure measurements are taken for each leg: one in the ankle (using the dorsalis pedis or posterior tibial artery) and one in the arm (using the brachial artery). The highest systolic pressure reading from the ankle is then divided by the highest systolic pressure reading from the arm.
For example, if the highest systolic blood pressure measured in the ankle is 120 mmHg and the highest systolic blood pressure measured in the arm is 130 mmHg, the ABI would be calculated as:
Example Calculation:
ABI = 120 mmHg / 130 mmHg = 0.92
Interpreting the ABI Results
The ABI value provides important insights into the health of your peripheral arteries:
ABI ≥ 1.00: This is considered normal. It indicates adequate blood flow to the legs and feet.
ABI between 0.91 and 0.99: This is borderline normal. Some consider a value between 0.75 and 0.90 as mild PAD.
ABI ≤ 0.90: This generally indicates PAD. The lower the ABI value, the more severe the blockage or narrowing of the arteries.
ABI ≤ 0.50: This is considered severe PAD and may indicate critical limb ischemia, a serious condition that can lead to non-healing wounds or gangrene.
ABI > 1.40: This may suggest calcified or hardened arteries, often seen in patients with diabetes or kidney disease. It can make the test less reliable.
Why is the ABI Important?
PAD is a significant risk factor for cardiovascular events such as heart attack and stroke, and it can also lead to mobility problems and limb pain. Early detection through the ABI test allows for timely intervention, including lifestyle modifications (like quitting smoking, exercise) and medical treatments (medications, angioplasty, or surgery) to manage the condition, improve circulation, reduce the risk of complications, and enhance the quality of life.
It is essential to have the ABI test performed by a qualified healthcare professional who can interpret the results in the context of your overall health history and other diagnostic findings.
function calculateABI() {
var highestAnkle = parseFloat(document.getElementById("highestSystolicAnkle").value);
var highestBrachial = parseFloat(document.getElementById("highestSystolicBrachial").value);
var resultElement = document.getElementById("abiResult");
var interpretationElement = document.getElementById("interpretation");
// Clear previous results
resultElement.textContent = "–";
interpretationElement.textContent = "";
// Validate inputs
if (isNaN(highestAnkle) || isNaN(highestBrachial)) {
resultElement.textContent = "Error";
interpretationElement.textContent = "Please enter valid numbers for both pressures.";
return;
}
if (highestAnkle < 0 || highestBrachial = 1.00 && abi = 0.91 && abi = 0.75 && abi = 0.50 && abi < 0.75) {
interpretationText = "Moderate PAD: Significant arterial narrowing.";
} else if (abi 1.40) {
interpretationText = "Inconclusive (Calcified Arteries): Suggests hardened arteries, test may be unreliable.";
} else {
interpretationText = "Interpretation unavailable for this value.";
}
interpretationElement.textContent = interpretationText;
}