How to use clinical signs and symptoms to estimate the probability of limb ischaemia in patients with a diabetic foot ulcer.

Assessment of ischaemia and interventions to improve perfusion are key elements in the management of the diabetic foot ulcer to achieve wound healing. This article will review, analyse and interpret the value of clinical information in determining the likelihood of limb ischaemia and thereby the need for referral to a vascular specialist. I conducted an historical review of the genesis of several currently recommended clinical signs and their diagnostic properties in the assessment of limb ischaemia. Changes in limb ischaemia probability based on such results were calculated using Bayes theorem, and the use of such probabilities is discussed in the context of the threshold approach to clinical decision making. Some clinical signs have negligible value in altering probability of limb ischaemia, possibly because they were advocated by Buerger for the diagnosis of thromboangiitis obliterans, an occlusive vascular disease of a different pathophysiology than atherosclerosis. Pedal pulse palpation, the most widely studied clinical sign, will marginally change a pre-test probability of ischaemia of 50% to 76% if positive (abnormal pulses) and to 36% if negative (normal pulses). Higher or lower pre-test probabilities of ischaemia will change the post-test probabilities such that these are too low or high to rule in or rule out ischaemia, respectively. Individual clinical signs convey little information regarding the presence of limb ischaemia but may have some value in combination or with pre-test probability near 50% in the assessment of ischaemia and the decision to refer for a vascular consultation.