Wound, Ostomy and Continence Nurses Society (WOCN) Practice Exam

How do you calculate the ABI?

1. Combine ankle and brachial pressures and divide by 2

2. Divide highest ankle pressure by highest brachial pressure

3. Subtract brachial from ankle pressure

4. Use only the resting pressure in the ankle

The correct answer is: Divide highest ankle pressure by highest brachial pressure

The correct method for calculating the Ankle-Brachial Index (ABI) involves dividing the highest ankle pressure by the highest brachial pressure. This calculation is essential for assessing peripheral arterial disease and determining the blood flow in the legs relative to the arms. To perform the calculation accurately, the following steps are typically taken: measure the systolic blood pressure in the ankle using a Doppler ultrasound or sphygmomanometer, and similarly, measure the highest systolic blood pressure in the arm (brachial artery). The ABI provides a comparative ratio that reflects the presence or absence of peripheral artery occlusion; a normal ABI is usually between 1.0 and 1.4, indicating adequate blood flow. This method is favored because it offers a clear understanding of arterial health by comparing pressures in these critical areas, and it has been validated by clinical research as an effective diagnostic tool. Other methods, like simply combining or subtracting pressures, do not yield the same meaningful information about vascular health and should not be utilized in the same context of evaluating arterial health.