American Board of Internal Medicine (ABIM) Certification Practice Exam

The ankle-brachial index (ABI) is calculated using which of the following pressures?

1. Femoral and brachial pressures

2. Dorsalis pedis and posterior tibialis pressures

3. Radial and ulnar artery pressures

4. Pulmonary and systemic arterial pressures

The correct answer is: Dorsalis pedis and posterior tibialis pressures

The ankle-brachial index (ABI) is specifically used to assess lower extremity arterial disease by comparing blood pressures in the lower leg to those in the arm. The correct calculation involves measuring the systolic blood pressures at the dorsalis pedis and posterior tibialis arteries in the ankle, and the systolic blood pressure at the brachial artery in the arm. Using the pressures from the dorsalis pedis and posterior tibialis arteries provides a direct assessment of the blood flow to the lower extremities, which is essential for determining the degree of peripheral vascular disease. The ABI is calculated by taking the highest ankle pressure (from either the dorsalis pedis or posterior tibialis) and dividing it by the highest brachial pressure. This ratio gives insight into how well blood is reaching the legs compared to the arms. Other options, such as using the femoral and brachial pressures, do not provide the crucial information regarding blood flow specifically to the ankles and are not appropriate for calculating the ABI. Measuring radial and ulnar artery pressures or comparing pulmonary and systemic arterial pressures also falls outside the context of assessing peripheral vascular disease, making them irrelevant for calculating the ABI.