Table 2. Projected Outcomes of Screening 100,000 Asymptomatic Adults for Carotid Artery Stenosis^a

^a. Screening and confirmatory testing assumptions were as follows: 1) The screening test is carotid duplex ultrasonography, with sensitivity for CAS 60% to 99% of 0.94 and specificity of 0.92; 2) the confirmatory test is none, cerebral angiography (sensitivity and specificity, 100%), or MRA (sensitivity, 0.95; specificity, 0.90); 3) the true prevalence is 1% in the general primary care population .65 years of age and 5% in high-risk patients; 4) the stroke complication rate with angiography is 1.2%; 5) all patients with positive test results go to surgery; 6) the perioperative stroke or death rate with CEA (whether the test result was true-positive or false-positive) is 3.1% (as in the Asymptomatic Carotid Surgery Trial [ACST]); 7) the perioperative nonfatal myocardial infarction rate with CEA (whether the test result was true-positive or false-positive) is 0.6% (as in ACST); 8) "events" are all strokes and perioperative deaths 5 years after CEA; 9) the probability of an event is 11.8% for medical and 6.4% for treatment with CEA (as in ACST); 10) one half of strokes prevented are nondisabling; and 11) no benefit is received from medical or CEA treatment for patients with false-positive screening test results.
CAS = carotid artery stenosis; CEA = carotid endarterectomy; MRA = magnetic resonance angiography; NNS = number needed to screen.

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