GRADING CAROTID STENOSIS WITH ULTRASOUND - AN INTERLABORATORY COMPARISON

Background and Purpose Carotid ultrasound had modest accuracy in the N orth American Symptomatic Carotid Endarterectomy Trial (NASCET) of car otid endarterectomy in predicting severe carotid stenosis when a 250-c m/s peak systolic velocity (PSV) criterion was applied to different la boratories. We compared the performance of two independent laboratorie s using similar equipment (ATL-HDI Ultramark 9) but different interpre tation criteria. Methods Consecutive patients who underwent both color -coded duplex ultrasound and intra-arterial digital subtraction angiog raphy were studied. PSV was determined with angle correction at the si te of the tightest arterial narrowing. Carotid stenosis was measured o n angiograms using the North American (N) method. Sensitivity, specifi city, and positive (PPV) and negative (NPV) predictive values with 95% confidence intervals were calculated for each laboratory. Results In 87 patients, 174 bifurcations were imaged. A 250-cm/s criterion was th e best single predictor of a >70% N stenosis at one laboratory (sensit ivity 93% [95% confidence interval, 85 to 101], specificity 86% [76 to 96], PPV 75% [62 to 87], and PPV 96% [90 to 102]) but had modest para meters at the other laboratory (50% [34 to 64], 87%, [77 to 97], 60 [4 4 to 76], and 91 [82 to 100], respectively). However, the diagnostic c riteria routinely used in the second laboratory included different vel ocity values, which when applied decreased specificity by 17% but incr eased sensitivity by 35% (85% [74 to 96], 70% [56 to 84], 90% [81 to 9 9], and 77% [64 to 90], respectively). Conclusions Despite the use of similar equipment, ultrasound grading of carotid stenosis is operator dependent and relies on different and individually validated criteria. Greater sensitivity of ultrasound screening is achieved by applying d iagnostic criteria specific to each laboratory. Multicenter studies sh ould use laboratory-specific criteria and a local validation process.