All Screening Tests Are Not Created Equal

Should you have your carotid arteries screened for plaque just because the test is available?

The carotid arteries are the large vessels in the neck that carry blood directly from the heart to the brain. Atherosclerosis, or plaque buildup, causes the narrowing of arteries (stenosis) and leads to reduced blood flow. Think of a pipe narrowed by debris, so the area available for fluid to flow is decreased. If that pipe is one of your carotids, blocking it with plaque can lead to a stroke, a leading cause of disability and death.

People are often approached to have ‘total body scanning’ or other vascular screening costing $100 or more out of pocket. This often includes a doppler or Duplex ultrasound of the carotids. This test estimates the degree of stenosis. However, the test results are quite dependent on the technician’s skill, so there are a fair number of false positives and false negatives with this procedure; i.e., people may be told they do have carotid disease when they don’t, or vice versa. Further testing may ensue based on these results.

A symptomatic individual with carotid stenosis might experience neurologic signs of a stroke – visual changes, difficulty with speech or language, weakness of an arm or limb, or periods of confusion. In a recent review, the Preventive Services Task Force tried to determine whether screening for carotid stenosis in patients without symptoms (asymptomatic) reduces the risk for stroke in those people. The study also tried to answer the question of what harm is associated with screening and interventions for carotid stenosis.

Review of available literature included studies comparing the use of medications to reduce atherosclerosis vs. surgery to remove plaque (carotid endarterectomy) vs. ballooning of the narrowed region of the artery and stent placement to keep it open. There was no difference in death rate among these three groups.

The disadvantages associated with screening involve whatever follow-up is done to evaluate a positive (abnormal) duplex ultrasound. For example, an abnormal ultrasound might lead a patient to have an angiogram (a study in which dye is injected into the carotid arteries to visualize flow) or surgery. An angiogram can cause bleeding, kidney failure, allergic reaction, damage to the artery and stroke. Carotid surgery can cause a heart attack, stroke, nerve damage, blood clot, pneumonia, etc. Missing a significant stenosis (i.e., a false negative) can lead to lack of intervention in someone who is at high risk for a stroke that may have been prevented.

The bottom line is that the test is not that accurate and there are risks to doing further procedures in those without symptoms who are at lower risk of stroke. Therefore, based on current knowledge, screening for asymptomatic carotid artery disease is not recommended. Check with your doctor for more information about your particular situation.

REFERENCE:
Screening for Asymptomatic Carotid Artery Stenosis: A Systematic Review and Meta-analysis for the U.S. Preventive Services Task Force. Annals of Internal Medicine. 2014;161:336-346.