Repeatability of Oscillometric Determinations of the Ankle-Brachial Index. The Atherosclerosis Risk in Communities (ARIC) Study

Background: The ankle-brachial index (ABI) is a noninvasive and inexpensive means to assess lower extremity artery patency with established validity. Low ABI values are predictive of cardiovascular morbidity and all-cause mortality. Automated, oscillometric devices are commonly used to measure ABI in population studies for timeefficiency and to reduce observer-dependent variability. The repeatability of multi-limb systolic blood pressure (SBP) and of ABI using oscillometric devices has not been evaluated in depth. Methods: Two examinations 4-8 weeks apart were conducted on 79 participants using standardized protocols. Using the VP-1000 Plus system bilateral systolic blood pressure (brachial and ankle) and ABI were measured twice five minutes apart, during each examination. The intra-class correlation coefficient (ICC), the corresponding 95% confidence intervals (95% CI), minimal detectable change (MDC95), and minimal detectable difference (MDD) were calculated. Results: The ICCs (95% CI) were 0.62 (0.49, 0.75) for right brachial SBP, 0.65 (0.53, 0.77) for left brachial SBP, 0.61 (0.48, 0.74) for right ankle SBP, 0.66 (0.55, 0.78) for left ankle SBP, 0.48 (0.34, 0.64) for right ABI, and 0.61 (0.48, 0.73) for left ABI. The MDC95 was 0.22 for right ABI, and 0.20 for left ABI. The MDD for two independent samples (N=100) was 0.06 for both right ABI and left ABI. Conclusion: The 4-8 week repeatability measures of the arm and ankle SBP, and of the left ABI are substantial, and the estimated repeatability of the right ABI is moderate. Reliability estimates based on this study can be used to correct for bias when using ABI.