Comparison of Automated Oscillometric Measurement of Ankle Brachial Index with Standard Doppler Measurement as a Screening Tool for Peripheral Artery Disease

Abstract

Objective —The use of continuous-wave Doppler ultrasound to determine ankle brachial index (ABI) is the gold standard for diagnosing asymptomatic peripheral artery disease. This method is labor intensive, requires training, and has considerable interobserver variability. Automated oscillometric measurement (AOM) of blood pressure is fast, simple, and generally available in clinics, but there are few studies of its usefulness for determination of the ABI. We compared these two methods to determine the usefulness of AOM as a screening tool. We also assessed the agreement between two different AOM devices. Methods —Seventy-four patients, including 33 diabetics, who presented to our vascular clinic to have their ABI measured were enrolled. A vascular nurse certified in ABI measurements (J.B.) performed blood pressure measurements in all four extremities by using the traditional Doppler method and two different automated oscillometric devices. The order of the three measurements was randomized. To avoid the effect of interrelated measures within each subject, we analyzed left and right legs separately (74 for each group). Measurements were grouped as abnormal (ABI = 0.90), normal (ABI 0.91–1.30), or elevated (ABI > 1.30). Agreement between Doppler measurements and oscillometric measurements was investigated by use of Pearson's χ2 analysis. In addition, correlation coefficients, including Spearman and Gamma statistic, were computed, as was the Kappa statistic, a measure of interrater agreement. Results —The correlation coefficients for comparison of Doppler with the two AOM devices were 0.70 and 0.73 ( p < 0.01). For the diabetics, correlation coefficients were 0.64 and 0.70 ( p < 0.01). The intermachine correlation ranged from 0.65 to 0.69 ( p < 0.01). As a screening tool oscillometric measurement had a sensitivity of 44%, specificity of 96%, positive predictive value of 87%, negative predictive value of 68%, and am accuracy of 73%. Kappa statistic was 0.41. Conclusions —Oscillometric measurement of ABI had good correlation with Doppler ultrasound measurements, and there was little difference between the two different machines tested. AOM has value as a rapid, initial screening examination in primary care clinics. When positive, the examination is a reliable indicator of atherosclerosis to identify patients who need intense risk factor modification. When negative, it is only moderately predictive of the absence of disease. Patients suspected of high risk for atherosclerosis who have negative examinations require further testing.