Abstract
BackgroundA low ankle-brachial index (ABI) is associated with increased risk of coronary heart disease, stroke, and death. Regression model parameter estimates may be biased due to measurement error when the ABI is included as a predictor in regression models, but may be corrected if the reliability coefficient, R, is known. The R for the ABI computed from DINAMAP™ readings of the ankle and brachial SBP is not known.MethodsA total of 119 participants in both the Atherosclerosis Risk in Communities (ARIC) study and the NHLBI Family Heart Study (FHS) had repeat ABIs taken within 1 year, using a common protocol, automated oscillometric blood pressure measurement devices, and technician pool.ResultsThe estimated reliability coefficient for the ankle systolic blood pressure (SBP) was 0.68 (95% CI: 0.57, 0.77) and for the brachial SBP was 0.74 (95% CI: 0.62, 0.83). The reliability for the ABI based on single ankle and arm SBPs was 0.61 (95% CI: 0.50, 0.70) and the reliability of the ABI computed as the ratio of the average of two ankle SBPs to two arm SBPs was estimated from simulated data as 0.70.ConclusionThese reliability estimates may be used to obtain unbiased parameter estimates if the ABI is included in regression models. Our results suggest the need for repeated measures of the ABI in clinical practice, preferably within visits and also over time, before diagnosing peripheral artery disease and before making therapeutic decisions.
Highlights
A low ankle-brachial index (ABI) is associated with increased risk of coronary heart disease, stroke, and death
At the time of the first ABI measure, the mean age was 61.3 years, mean weight 75.7 kg, mean body mass index 28.0 kg/m2, and mean ABI 1.16; 13 (10.9 percent) had diabetes mellitus, 43 (36.1 percent) had hypertension, and 31 (26.0 percent) had coronary heart disease. Characteristics of this group were similar to those of the Atherosclerosis Risk in Communities (ARIC) cohort in Minneapolis and Forsyth County at the time of the ARIC baseline survey and at visit 3, except with respect to the distribution of characteristics related to the Family Heart Study (FHS) sampling procedures: race/ethnicity, field center, and CHD prevalence (Table 1)
The estimated reliability coefficient for the ankle systolic blood pressure (SBP) was 0.682 (95 percent confidence interval (CI): 0.570, 0.772), The ankle SBP increased an average of 3.1 mmHg between the first and second measures (p = 0.11), which resulted in a statistically significant average increase of 0.031 in the ABI (p = 0.02)
Summary
A low ankle-brachial index (ABI) is associated with increased risk of coronary heart disease, stroke, and death. Regression model parameter estimates may be biased due to measurement error when the ABI is included as a predictor in regression models, but may be corrected if the reliability coefficient, R, is known. The ABI has been shown in cross-sectional studies to be associated with cardiovascular disease (CVD) risk factors including smoking [10,11,12,13,14,15,16,17] diabetes [10-. The parameter estimate for a regression model with a single explanatory variable measured with error will be biased towards the null by a multiplicative factor R, the reliability coefficient. Unbiased parameter estimates may be obtained using Stein estimators of true values [36] or other techniques if R is known [34,35]
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