A new test based on ultrasound scans may be able to spot people at high risk of a stroke, though it is still too early to be excited, researchers said.

Nearly 800,000 people suffer strokes each year in the United States alone, with about a sixth of them dying of it and many more left disabled.

The study, though, is able to separate people who have clogged neck, or carotid, arteries into those who are relatively likely to suffer a stroke and those who aren't, which may help decide who would benefit from a controversial surgery in which doctors clean out cholesterol buildups blocking the artery.

"Our study suggests that we can identify those few subjects who are candidates for carotid surgery due to their high risk despite best medical treatment," said Raffi Topakian, at the Academic Teaching Hospital Wagner-Jauregg in Linz, Austria, whose findings appear in Neurology.

"Of course, it's still too early to be enthusiastic about our findings. Ideally, our findings should be corroborated by other studies."

The test is based on two types of ultrasound scans, one of the carotid arteries that supply blood to the brain, and one of the arteries in the brain itself.

Both are readily available at hospitals, although the brain scan takes about an hour and is not easy to interpret.

Currently, in the U.S. and Canada, too many patients get surgery to clean out the cholesterol buildup despite having few symptoms, said Lars Marquardt, a neurologist at the University of Erlangen-Nuremberg in Germany, who wrote an editorial about the findings.

In the study, 428 symptom-free patients with clogged carotid arteries, so-called carotid stenosis or plaque, had both scans done and were then followed for two years.

Of those who started out with warning signs on both scans, the yearly stroke risk was nine percent.

Those without suspicious-looking results on the two scans—about 94 percent of the patients—had a risk of less than one percent per year.

Clogged carotid arteries are a risk factor for stroke, but many doctors believe doing the surgery is too hazardous for symptom-free people at average risk.

"There is a subset of patients who need it, and this new test will probably —I'm sure it will—help identify those. It wasn't a huge study, but it is very promising," said Marquardt.

Overall, only about two percent of people with symptom-free carotid stenosis suffer a stroke per year when their condition is managed with drugs and lifestyle changes.

By contrast, carotid surgery performed by experienced surgeons triggers a fatal stroke in as many as three percent.

"There is a very important story to be told about unnecessary carotid surgery and stenting in the U.S.," said David Spence, a stroke prevention researcher at the University of Western Ontario in London, Canada.

"Ninety-five percent of these procedures are for asymptomatic stenosis, and our work shows that 90 percent of these patients would be better off without surgery."

For this sort of reason, the U.S. Preventive Services Task Force, a federally funded expert panel, recommends against screening for carotid stenosis in the first place.

"If you are screening lots of people who have plaques, there's an awful lot of harm associated with that," said Patrick O'Malley of the Uniformed Services University in Bethesda, Maryland, adding that the new test could lead to more screening for carotid stenosis, which hasn't been shown to cut stroke rates.

Harms from screening include getting unnecessary surgeries and medications, which have complications and side effects, a drawback Topakian acknowledged.

"The tests are practically risk free, the consequences are not," he added.