PERFORMANCE OF CAROTID ULTRASOUND IN EVALUATING CANDIDATES FOR CAROTID ENDARTERECTOMY IS OPTIMIZED BY AN APPROACH BASED ON CLINICAL OUTCOMERATHER THAN ACCURACY

Background and Purpose The best method of selecting endarterectomy can didates for cerebral angiography is controversial. Carotid duplex ultr asound (CDUS) is widely used, but its performance varies across instit utions. The clinical utility of CDUS could be improved with lest crite ria based on patient outcome rather than test accuracy. Methods In 155 carotid bifurcations studied by CDUS and cerebral angiography, the de gree of angiographic stenosis was measured by a reader, blinded to CDU S, using the North American Symptomatic Carotid Endarterectomy Trial ( NASCET) method. We calculated accuracy, sensitivity, and specificity f or predicting greater than or equal to 70% angiographic carotid stenos is of different peak systolic frequencies (PSF) measured by CDUS and g enerated a receiver operator characteristic (ROC) curve. We used NASCE T outcome data and published data on angiographic complications to def ine relative ''costs'' of false-positive and false-negative CDUS, and we determined the point on the ROC curve representing the CDUS criteri on with the highest clinical utility. We compared projected morbidity and mortality rates for 1000 hypothetical endarterectomy candidates re sulting from the use of the most accurate CDUS criterion versus the CD US criterion with the highest clinical utility by ROC analysis. Result s While PSF greater than or equal to 8 kHz had the highest CDUS accura cy (93%), its projected stroke and death rate due to CDUS error was 10 .4/1000. On the other hand, PSF greater than or equal to 7 kHz, define d by ROC analysis to have the highest clinical utility, had a lower mo rbidity and mortality rate of 6.8/1000. Conclusions The use of ROC ana lysis and available outcome data can improve the performance of CDUS i n selecting endarterectomy candidates for cerebral angiography.