Screening for carotid artery stenosis has become an issue because prior studies have shown a small reduction in the risk of stroke if asymptomatic, significant carotid artery stenosis is treated surgically. Evidence suggests that relieving carotid artery blockage can reduce the risk of stroke by 5% over 5 years (about 1% per year). While this risk reduction is certainly modest at best, it has enticed many doctors to routinely perform screening with non-invasive ultrasound in individuals who are at risk for this disease.
But the USPSTF has concluded that such non-invasive screening can lead to more harm than good in many patients, and that for the population as a whole, screening should be avoided.
The obvious question is: What harm can non-invasive screening do? As it turns out, quite a bit. A big problem with the ultrasound test is that it produces many false positive exams. That is, it declares blockages to be present when there are none. So, when an ultrasound test is positive, generally an invasive angiographic study is required to confirm the diagnosis - a test that carries its own risk of bleeding, infection, and even stroke. Alternately, the patient may be sent for an MRI study to confirm the diagnosis - but MRI studies of the carotid artery also carry a risk of being falsely positive, in which case surgery would be recommended needlessly. And the surgery itself, in the very best centers, produces a 3% 30-day risk of stroke.
The USPSTF concludes "for individuals with asymptomatic carotid artery stenosis, there is moderate certainty that the benefits of screening do not outweigh the harms."
While I can certainly think of individuals for whom I would ignore this recommendation (the patient, for instance, with a strong family history of stroke and clear evidence of widespread vascular disease, in whom a positive ultrasound screen is much more likely to be a true positive), in general the recommendation is sound. What is needed, obviously, is a non-invasive screening test that is more accurate than the ultrasound. Until then, doctors ought to use available screening methods judiciously.