The diagnostic value of colour duplex ultrasound for symptomatic carotid stenosis in clinical practice

We assessed the accuracy of colour duplex ultrasound for the detection of s evere (70-99 %) symptomatic carotid stenosis in a clinical setting, in orde r to assess whether it could make carotid angiography unnecessary. In 152 p atients with a transient ischaemic attack or nondisabling ischaemic stroke in the carotid distribution, we compared the degree of colour duplex ultras ound stenosis with angiographic stenosis by receiver-operating-characterist ic analysis. The angiograms were evaluated by blinded observers, and compar ed with routine reports of the colour duplex examination. We computed the s ensitivity and specificity of colour duplex, and the number of angiograms a nd sonographic studies needed to prevent one stroke within 3 years, taking into account the risks of angiography, and the risks and efficacy of endart erectomy. The estimates were adjusted for nonverification bias. We found 34 patients (22 %) with a severe (70-99 %) symptomatic carotid stenosis, In 1 6 patients (11 %)the symptomatic artery was occluded. The sensitivity and s pecificity of duplex ultrasound were 76 % and 85 %, respectively. The numbe r of patients needed to undergo angiography to prevent one stroke was reduc ed from almost 200 to 33, when colour duplex was used as a preoperative exa mination. After adjustment for the effects of nonverification, the sensitiv ity dropped to 58 % and the number of duplex studies needed to prevent one stroke would double. The number of angiograms needed after positive duplex sonography would be virtually unaffected. Were colour duplex sonography to have been the sole preoperative investigation, the number needed to diagnos e to prevent one stroke within 3 years would be approximately 350, more tha n twice as many as with the combined diagnostic strategy. The diagnostic ac curacy of colour duplex sonography in clinical practice seems less impressi ve than previous studies have suggested, but it remains an effective way to select patients for angiography. Its use as a single pre-operative assessm ent cannot be recommended.