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Comparison of Accuracy of Two Different Methods to Determine Ankle-Brachial Index to Predict Peripheral Arterial Disease Severity Confirmed by Angiography
Study Questions:
What is the predictive ability of two different methods for calculating the ankle-brachial index (ABI) for the diagnosis of peripheral artery disease (PAD)?
Methods:
Between July 2005 and June 2010, 130 patients (260 limbs) who underwent ABI testing and arteriography of the lower extremities within 6 months of one another at a single center were assessed. Patients with prior lower extremity bypass surgery or stenting were excluded. Angiographic stenosis was categorized for each limb (0-49%, 50-75%, and 76+%) and a scoring system was used to calculate the degree of stenosis of the lower extremity. The ABI was calculated in two manners, one method using the lower of the dorsalis pedis and posterior tibial arteries (LABI) and the other method using the higher pressure (HABI). Each of those pressure measurements were divided by the higher pressure measures in each of the two brachial arteries of the upper extremities to generate the ABI value. An ABI <0.9 was considered abnormal. Linear regression was performed to assess the degree of angiographic stenosis with the ABI measurement while controlling for clinical predictors of PAD, such as age, gender, diabetes, hypertension, smoking history, and coronary artery disease.
Results:
The ABI was abnormal in 68% of patients using the HABI method compared to 84% of patients when using the LABI method. Sensitivity and accuracy measurements were higher for the LABI (90% sensitive, 83% accurate) compared to HABI (75% sensitive, 73% accurate) for the detection of segment with at least 50% angiographic stenosis. These finding persisted in the subgroup of patients with known diabetes. Specificity was higher when using the HABI calculation (63%) rather than the LABI calculation (47%) for detecting 50+% stenosis. Regression analysis demonstrated improved predictive ability for the degree of PAD burden in the LABI (odds ratio [OR], 5.3; 95% confidence interval [CI], 1.6-16) compared to the HABI (OR, 3.4; 95% CI, 1.2-10) technique.
Conclusions:
The authors concluded that the LABI method has superior sensitivity and is a better predictor of PAD severity than the HABI method.
Perspective:
This single-center study challenges the conventional practice of using the higher lower extremity pressure measurement (HABI) when calculating the ABI for PAD screening. The American Heart Association 2012 guideline on the measurement and interpretation of the ABI recommends using the HABI based on the results of two prior studies. Both of those studies concurred with this report that use of the LABI demonstrated better sensitivity than the HABI value. However, they favored the use of the HABI value because its specificity was reported to be greater than the LABI in both studies, which was also shown in this report. Understanding the goal of a study and its impact on “ruling in” (specificity) or “ruling out” (sensitivity) a disease is important when determining which ABI value to use. Clinicians should be aware that stark differences between the pressures in each of the lower extremity arteries might be a marker for clinically significant PAD that warrants further investigation.
Keywords: Coronary Artery Disease, Brachial Artery, Ankle Brachial Index, Peripheral Arterial Disease, Constriction, Pathologic, Cost of Illness, Peripheral Vascular Diseases, Smoking, Tibial Arteries, Diabetes Mellitus, Hypertension
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