Ankle/Brachial Pressure Indices - Now of Limited Value
Ankle-brachial pressure indices (ABIs) served the vascular laboratory well prior to widespread introduction of duplex scanning, but we consider that they are now irrelevant for patients with occlusive atherosclerotic disease. ABIs are frequently performed to detect disease - a careful history and examination should distinguish arterial disease from other pathology just as well. ABIs may be requested to decide whether a patient requires a duplex scan and if this needs to be for one side or both - duplication of time and expense to perform both in many patients is less efficient than going straight to the duplex scan alone in all. Complete examination for ABIs at rest and following exercise is a time-consuming, expensive investigation with little reward - an experienced sonographer can perform a full bilateral lower limb arterial duplex scan in about the same time. Interobserver variability for ABIs is high. ABIs tell no more than whether or not there is reduced pressure due to a stenosis or occlusion. There is little correlation between ABIs and the severity of clinical disease. There is no correlation with measured walking distances. Attempts to define critical ischaemia based on ABIs or ankle pressures failed. Nor is there correlation between ABIs and the site of disease. Far more anatomical and physiological information is gained from the duplex scan. Reduced ABIs relate to future risk of cardiac and cerebrovascular events and this may warrant screening. ABIs are valuable to investigate arterial entrapment syndromes. However, we stopped recommending ABIs for patients with lower limb occlusive arterial disease long ago.