Benefits and risks of screening people for > 60% asymptomatic carotid stenosis in different prevalence groups: best case scenario
| Prevalence (%) | Ultrasound to angiogram to surgery | Ultrasound to MRA to surgery | Ultrasound direct to surgery | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Ratio benefit: harm | Net strokes prevented/ 10 000 screened | Strokes or deaths in false positives/ 10 000 screened1-150 | Ratio benefit: harm | Net strokes prevented/ 10 000 screened | Strokes or deaths in false positives/ 10 000 screened1-150 | Ratio benefit: harm | Net strokes prevented/ 10 000 screened | Strokes or deaths in false positives/ 10 000 screened1-150 | |||
| 1 | 0.7 | −4 | 8 | 3.8 | 5 | 0.5 | 0.6 | −4 | 10 | ||
| 5 | 1.8 | 16 | 8 | 4.9 | 28 | 0.5 | 2.2 | 20 | 10 | ||
| 10 | 2.2 | 40 | 8 | 5.1 | 56 | 0.5 | 3.4 | 50 | 9 | ||
| 20 | 2.6 | 88 | 7 | 5.2 | 112 | 0.4 | 4.0 | 110 | 8 | ||
| 25 | 2.6 | 112 | 6 | 5.2 | 141 | 0.4 | 4.3 | 141 | 8 | ||
Assumptions: ultrasound sensitivity and specificity 93% each; MRA sensitivity and specificity 95% each; surgical risk of stroke or death=1.5%; angiographic risk of stroke or death=1.2%; reduction in risk of ipsilateral stroke for true positive severe stenosis from 11% to 3% over five years.
↵1-150 Number of angiographic or surgical strokes or deaths caused in people who are false positives/10 000 screened.