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.interpretation.severe { color: #dc3545; }
.interpretation.unclear { color: #6c757d; }
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Understanding the Ankle-Brachial Index (ABI)
The Ankle-Brachial Index (ABI) is a simple, non-invasive diagnostic test used to assess the blood circulation in the legs. It compares the systolic blood pressure measured at the ankle with the systolic blood pressure measured at the arm. A lower ABI suggests that there may be a narrowing or blockage in the arteries of the legs, a condition known as peripheral artery disease (PAD).
How is the ABI Calculated?
The calculation is straightforward. The ABI is the ratio of the systolic blood pressure in the ankle to the systolic blood pressure in the arm. Typically, the highest systolic pressure is used from either the dorsalis pedis or posterior tibial artery at the ankle, and the highest systolic pressure is used from either brachial artery in the arm.
The formula for calculating ABI for each leg is:
ABI = (Systolic Blood Pressure in Ankle) / (Systolic Blood Pressure in Arm)
This calculation is performed separately for the right leg and the left leg, using the highest ankle pressure on that side and the highest arm pressure.
Interpreting ABI Results
The ABI value provides crucial information about the health of your peripheral arteries:
- ABI ≥ 1.00 to 1.40 (Normal): Indicates adequate blood flow and no significant arterial narrowing in the legs. An ABI slightly above 1.0 might be acceptable, but values much higher than 1.40 can sometimes indicate non-compressible arteries (e.g., due to calcification), which might require further investigation.
- ABI < 1.00 to 0.90 (Mild PAD): Suggests mild peripheral artery disease. This indicates some degree of arterial narrowing, which might lead to symptoms during exercise (like claudication – leg pain when walking).
- ABI < 0.90 to 0.70 (Moderate PAD): Suggests moderate peripheral artery disease. This indicates more significant blockages, and symptoms may be present even at rest or with less activity.
- ABI < 0.70 (Severe PAD): Indicates severe peripheral artery disease. This suggests critical limb ischemia, a serious condition that can lead to non-healing wounds, rest pain, and even amputation if not treated promptly.
- ABI > 1.40 (Non-compressible Arteries): This value usually means the arteries in the ankle are too stiff (calcified) to be compressed by the blood pressure cuff. This often occurs in individuals with diabetes or chronic kidney disease. While not directly indicative of PAD severity, it signifies vascular disease and may necessitate alternative diagnostic methods.
It's important to note that a normal ABI does not entirely rule out PAD, especially in individuals with certain conditions or atypical symptoms. The ABI is a screening tool, and its results should always be interpreted by a qualified healthcare professional in the context of a patient's overall medical history and physical examination.
Why is the ABI Important?
Peripheral Artery Disease (PAD) is a common circulatory problem in which narrowed arteries reduce blood flow to the limbs, most commonly the legs. PAD is a marker of systemic atherosclerosis, meaning it's a sign of widespread hardening and narrowing of the arteries throughout the body, which significantly increases the risk of:
- Heart attack
- Stroke
- Coronary artery disease
- Limb amputation
Regular screening with the ABI, especially for individuals with risk factors such as smoking, diabetes, high blood pressure, high cholesterol, or a family history of PAD, can help detect PAD early. Early detection allows for timely intervention, lifestyle modifications, and medical treatment to manage the disease, reduce cardiovascular risk, and prevent severe complications.
function calculateABI() {
var systolicRightArm = parseFloat(document.getElementById("systolicRightArm").value);
var systolicLeftArm = parseFloat(document.getElementById("systolicLeftArm").value);
var systolicRightAnkle = parseFloat(document.getElementById("systolicRightAnkle").value);
var systolicLeftAnkle = parseFloat(document.getElementById("systolicLeftAnkle").value);
var resultContainer = document.getElementById("resultContainer");
var abiResult = document.getElementById("abiResult");
var abiInterpretation = document.getElementById("abiInterpretation");
if (isNaN(systolicRightArm) || isNaN(systolicLeftArm) || isNaN(systolicRightAnkle) || isNaN(systolicLeftAnkle) ||
systolicRightArm <= 0 || systolicLeftArm <= 0 || systolicRightAnkle <= 0 || systolicLeftAnkle = 1.00 && finalABI <= 1.40) {
interpretation = "Normal";
interpretationClass = "normal";
} else if (finalABI = 0.90) {
interpretation = "Mild PAD";
interpretationClass = "mild";
} else if (finalABI = 0.70) {
interpretation = "Moderate PAD";
interpretationClass = "moderate";
} else if (finalABI 1.40) {
interpretation = "Non-compressible Arteries";
interpretationClass = "unclear";
} else {
interpretation = "Unclear/Invalid Calculation";
interpretationClass = "unclear";
}
// Format the ABI value to two decimal places
var formattedABI = finalABI.toFixed(2);
abiResult.textContent = formattedABI;
abiInterpretation.textContent = interpretation;
abiInterpretation.className = "interpretation " + interpretationClass; // Update class for styling
resultContainer.style.display = "block";
}