Journal of General Practice

What is the Potential for False Positive Results in Ankle Brachial Index Measurements Performed by Emergency Providers?

Abstract

George L Higgins

Introduction: The Ankle-Brachial Index measurement (ABI) is an easily performed bedside test used to screen for lower extremity arterial injury. It is possible that the ABI is not always correctly performed in the acute setting, depending on available equipment and provider familiarity with validated measurement techniques. We sought to determine the potential for false positive ABI results in healthy subjects if the ABI is performed incorrectly. We also sought to identify the method most likely to minimize false positive results. Materials and methods: Healthy volunteers and low acuity emergency department patients were enrolled. Exclusion criteria included a known history of documented peripheral arterial disease or extremity trauma. Subjects were examined by two investigators. “Most Accurate” (MA) ABI measurements used the higher of the two ankle readings and the higher of the two brachial readings to calculate the result. “Least Accurate” (LA) measurements used the lower of the two ankle readings and the higher of the two brachial readings. Results: 118 study subjects were enrolled: mean age 32.8 years (range 19 to 49), 50% female, none with known peripheral vascular disease or extremity trauma, and none with documented femoral artery bruit at the time of the study. When a single provider performed LA ABI’s, the false positive rate was 29%, while single provider MA ABI’s lowered the false positive rate to 2%. For two provider ABI’s, these rates were 4% and 0%, respectively. Conclusions: We identified an unacceptably high rate of false positive ABI results if the test is performed incorrectly. We recommend strict adherence to standardized ABI measurement protocols to minimize this error. Ideally, an ABI measurement of less than 0.9 in a patient with lower extremity trauma should be confirmed by a second provider in order to minimize the risk of inappropriately implementing invasive diagnostic procedures.