Accuracy of carotid duplex is laboratory specific and must be determined by internal audit

Objective: To assess the accuracy of carotid duplex in a single vascular laboratory at the prediction of an angiographic 70% internal carotid artery stenosis. Design: A retrospective review of all patients who underwent both carotid duplex and angiography in a 1-year period at a vascular unit which participates in the ACST trial. Methods: Peak systolic velocity was used as a primary end-point in carotid duplex examinations with a PSV > 130 cm/s used as an indication for angiographic assessment. Biplanar arch aortography and selective carotid catheterisation were performed as indicated and diameter reduction calculated by the ECST method. Results: The sensitivity of 130 cm/s for the detection of a 70% stenosis was 96% and the specificity 67%. If a PSV of 250 cm/s were used the sensitivity would be only 37% and specificity 96%. Conclusions: Applying duplex criteria from one centre to another is inappropriate. Laboratory specific audit of duplex and angiography is essential before deciding to abandon preoperative angiography for carotid disease.