Background: The aim of this study was to determine the risk factors for conversion from a normal to either a low or high ankle-brachial index (ABI).
Methods: Participants in the Multi-Ethnic Study of Atherosclerosis who had two separate measurements of the ABI over a 3-year time period were assessed.
Results: At baseline, the mean age was 62 years and 50% were women, 28% African American, 12% Chinese, 22% Hispanic and 38% non-Hispanic White. Of the 5514 participants with a baseline ABI between 0.90 and 1.40, 89 (1.6%) had an ABI < or = 0.90 ("low ABI group") and 71 (1.3%) had an ABI > or = 1.40 ("high ABI group") 3 years later. On multivariable analysis, the odds for having progressed into the low ABI group were significantly increased for higher baseline age, hypertension, diabetes, greater pack-years of cigarette smoking, and homocysteine levels. The odds for progression into the high ABI group were increased for male gender and higher body mass index. Compared with non-Hispanic Whites, African Americans had a significantly higher odds for progression to the low ABI group (odds ratio [OR]: 2.24, 95% confidence interval [CI]: 1.29-3.88) while having a reduced odds for progression to the high ABI group (OR: 0.50, 95% CI: 0.24-1.00). Neither Chinese nor Hispanic ethnicity was significantly associated with progression to either ABI group.
Conclusions: The risk factors for progression to a low or high ABI were distinct and African Americans were at increased risk for progression to a low ABI but at decreased risk for progression into the high ABI group.