The Ankle Brachial Index Is Associated with Leg Function and Physical Activity: The Walking and Leg Circulation Study

BACKGROUND: The ankle brachial index (ABI) is a noninvasive, reliable measure of lower-extremity ischemia. However, the relationship between ABI and lower-extremity function has not been well studied. OBJECTIVE: To describe the association between the ABI and lower-extremity function. DESIGN: Cross-sectional study. SETTING: 3 academic medical centers in the Chicago area. PARTICIPANTS: 740 men and women (460 with peripheral arterial disease). MEASUREMENTS: Accelerometer-measured physical activity over 7 days, 6-minute walk, 4-m walking velocity, standing balance, and ABI. RESULTS: 33% of participants with peripheral arterial disease had intermittent claudication. Fewer than 40% of participants with an ABI less than 0.40 walked continuously for 6 minutes compared with more than 95% of participants with an ABI between 1.00 and 1.50. Compared with an ABI of 1.10 to 1.50, an ABI less than 0.50 was associated with shorter distance walked in 6 minutes (beta-regression coefficient = -523 ft 95% CI, -592 to -454 ft; P < 0.001), less physical activity (beta = -514.8 activity units CI, -657 to -373 activity units; P < 0.001), slower 4-m walking velocity (beta = -0.21 m/s CI, -0.27 to -0.15 m/s; P < 0.001), and less likelihood of maintaining a tandem stand for 10 seconds (odds ratio, 0.37 CI, 0.18 to 0.76; P = 0.007), after adjustment for typical confounders. Associations between ABI and function were stronger than associations between leg symptoms and function. CONCLUSIONS: The ABI, a noninvasive test that can be performed in a medical office, is more closely associated with leg function in persons with peripheral arterial disease than is intermittent claudication or other leg symptoms. These data support the use of the ABI to identify abnormal lower-extremity function.