February 24, 2020
Study Highlights Limitations of Resting ABI in the Diagnosis of Symptomatic PAD
February 24, 2020—The Society for Vascular Surgery (SVS) announced that findings from a large, single-center study highlight the limitations of using the resting ankle-brachial index (ABI) in the diagnosis of symptomatic peripheral arterial disease (PAD), particularly in those with diabetes mellitus (DM) and chronic kidney disease (CKD). The study by vascular surgeon Ali AbuRahma, MD, and investigators from West Virginia University in Morgantown, West Virginia, will be published in the March edition of SVS’s Journal of Vascular Surgery.
In the SVS press release, Dr. AbuRahma commented, “Because of the sometimes-artefactual elevation in resting ABIs, it is not uncommon to miss the diagnosis of PAD in patients with DM and CKD during ABI screening. As a result, patients with symptomatic PAD but an ABI within the normal range may be deprived of the benefits of intervention.” Dr. AbuRahma continued, “The present study confirmed that a normal ABI can mask the presence of PAD of the lower extremities of symptomatic patients with PAD with < 50% stenosis by duplex ultrasound (DUS). The addition of the toe-brachial index (TBI), particularly in those with inconclusive ABIs, appears to increase the accuracy of this noninvasive evaluation.”
As noted by SVS, the ABI is an important part of the noninvasive evaluation of patients suspected to have PAD and that because of its commonality, particularly its ease of use in an office setting, some clinicians and nonvascular specialists heavily rely on the ABI to rule out the diagnosis of PAD. However, patients at high risk for the development of PAD, including patients with DM and CKD, may have falsely elevated ABIs caused by noncompressible lower extremity arteries. In these cases, blind reliance on the results of the ABI can lead to misdiagnosis and mistreatment of patients with symptomatic PAD.
In the current study, the investigators quantitatively addressed this problem by retrospectively evaluating their large, single-center, prospectively collected noninvasive vascular database.
The study included 2,226 ABIs and 1,383 DUS examinations in patients with symptomatic PAD. In this study population, the prevalence of DM was 46% and CKD was 16%.
As summarized by SVS, for patients with limb-threatening ischemia, the resting ABIs were: 40% normal, 40% abnormal, and 20% inconclusive.
In detecting a > 50% stenosis by DUS in symptomatic patients, the sensitivity of the ABI was 57% (95% confidence interval [CI], 54%–61%) in the overall series; 51% (95% CI, 46–56%) in DM patients; and 43% (95% CI, 34%–53%) in CKD patients.
The value of adding the TBI in detecting a > 50% stenosis in this series was also evaluated. The sensitivity of this test was 85% (95% CI, 79%–90%) in the overall series; 84% (95% CI, 76%–90%) in DM patients; and 77% (95% CI, 61%–88%) in CKD patients.
The SVS announcement closed with commentary saying, “Blind reliance on screening tests is dangerous. This study underscores the importance of understanding the limitations of using the resting ABI in the diagnosis of symptomatic PAD, especially in patients prone to having falsely elevated results such as in diabetics and those with kidney disease.”