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A focal ipsilateral carotid bruit had a sensitivity of 63%and a specificity of 61%for high-grade stenosis and,when absent,only lowered the probability for high-grade stenosis from a pretest value of 52%to a post- test probability of 40%.When combined with four other clinical characteristics(an infarction on computed tomography6 of the head,a carotid ultrasound scan suggesting more than 90%stenosis,a transient ischemic attack rather than a minor stroke as a qualifying event,and a retinal rather than a hemispheric qualifying event),the predicted probabilities of high-grade stenosis ranged from a low of 18%(when none of the features was present)to a high of 94%(when all the features were present).Cervical bruits alone were not sufficiently predictive of high- grade symptomatic carotid stenosis to be useful in selecting patients for angiography;they were absent in over one third of patients with high-grade stenosis.When combined with other clinical variables,patients with high or low probabilities of 70%to 99%stenoses could be identified,but this prediction model still missed many individuals with high-grade stenosis, even in this training set of selected patients. |
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