Measurement error of percent diameter carotid stenosis determined by conventional angiography: implications for noninvasive evaluation.

BACKGROUND AND PURPOSE Our aim was to quantitate the range of error in measurement of percent diameter carotid stenosis using conventional angiography in order to estimate the misclassification rate in selecting patients for carotid endarterectomy. METHODS A secondary or meta-analysis of published data regarding carotid stenosis measurement error associated with angiography yielded a narrow range of standard deviation across several studies using different measurement protocols. A simulation of the measurement process was developed to model this error and allow estimation of misclassification rates compared with true values for stenosis. RESULTS A standard deviation of 8% describes the average error observed at 60% diameter stenosis across a number of studies. Using the measurement model, for a population with 30% prevalence of 60% stenosis, this finding implies a misclassification rate of approximately 4% overall for conventional angiography. CONCLUSION Like all diagnostic tests, angiography is associated with measurement error. This does not affect the results of carotid stenosis therapy trials using angiography but does need to be taken into account when evaluating noninvasive alternative tests for carotid stenosis.