Different methods of calculating ankle-brachial index in mid-elderly men and women: the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

The ankle-brachial index (ABI) is a marker of subclinical atherosclerosis related to health-adverse outcomes. ABI is inexpensive compared to other indexes, such as coronary calcium score and determination of carotid artery intima-media thickness (IMT). Our objective was to identify how the ABI can be applied to primary care. Three different methods of calculating the ABI were compared among 13,921 men and women aged 35 to 74 years who were free of cardiovascular diseases and enrolled in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil). The ABI ratio had the same denominator for the three categories created (the highest value for arm systolic blood pressure), and the numerator was based on the four readings for leg systolic blood pressure: the highest (ABI-HIGH), the mean (ABI-MEAN), and the lowest (ABI-LOW). The cut-off for analysis was ABI<1.0. All determinations of blood pressure were done with an oscillometric device. The prevalence of ABI<1% was 0.5, 0.9, and 2.7 for the categories HIGH, MEAN and LOW, respectively. All methods were associated with a high burden of cardiovascular risk factors. The association with IMT was stronger for ABI-HIGH than for the other categories. The proportion of participants with a 10-year Framingham Risk Score of coronary heart disease >20% without the inclusion of ABI<1.0 was 4.9%. For ABI-HIGH, ABI-MEAN and ABI-LOW, the increase in percentage points was 0.3, 0.7, and 2.3%, respectively, and the relative increment was 6.1, 14.3, and 46.9%. In conclusion, all methods were acceptable, but ABI-LOW was more suitable for prevention purposes.