The healthcare provider asked me to measure the ankle-brachial index (ABI) in my patient with intermittent claudication. What's the purpose of this test and how do I perform it?-T.S., N.M.
Melissa Moye, BSN, RN, CCRN, replies: The ABI is a noninvasive and easy-to-perform screening tool used to assess for the presence of lower extremity peripheral artery disease (PAD). Patients with PAD present with distinct syndromes, including classic or intermittent claudication, described as lower extremity fatigue, aching, numbness, or pain in the buttock, thigh, calf, or foot with a consistent (reproducible) onset, with exercise and relief with rest.1
Risk factors for lower extremity PAD include:
* age younger than 50 in patients who have diabetes and one additional risk factor, such as smoking, dyslipidemia, hypertension, or hyperhomocysteinemia
* ages 50 to 69 in patients with a history of smoking or diabetes
* age 70 or older
* leg symptoms with exertion (suggesting claudication) or ischemic rest pain
* an abnormal lower extremity pulse exam
* atherosclerotic coronary, carotid, or renal artery disease.1
To perform an ABI, ask the patient to lie supine for 5 minutes or more while you gather standard BP cuffs, a handheld Doppler, and ultrasound gel. Put a BP cuff on the patient's right ankle and one on the right arm. After applying the gel, use the Doppler to measure the patient's systolic pressure in the right arm. Next, use the Doppler to measure dorsalis pedis (DP) and posterior tibial (PT) systolic pressures. Repeat this procedure for the patient's left ankle and arm. Using the higher ankle pressure (DP or PT) for each lower extremity and the higher arm pressure, calculate the ratio of each ankle to brachial pressure using this formula:
Higher ankle pressure (DP or PT)/Higher arm pressure (of either arm).
The ABI is interpreted as follows:
* 1.00 to 1.29: normal
* 0.91 to 0.99: borderline
* 0.41 to 0.90: mild to moderate disease
* less than or equal to 0.40: severe disease.1
Depending on your patient's ABI results, additional diagnostic testing may be needed.