One out of every eight strokes is preceded by a "warning stroke," which is a transient ischemic attack (TIA) or mild stroke, according to research published in the September 29, 2009, print issue of Neurology®, the medical journal of the American Academy of Neurology.

"These results illustrate the need for better risk assessment tools for preventing strokes before they occur," said study author Daniel G. Hackam, MD, PhD, of the University of Western Ontario in London, ON. "Other studies have shown that up to 80 percent of strokes after TIA can be prevented when risk factors are managed intensively."

For the study, researchers identified all people at Ontario hospitals with a diagnosis of stroke over four years. Of the 16,400 patients, 2,032, or 12.4 percent, had a TIA prior to the stroke. During a TIA, stroke symptoms last for less than 24 hours and then resolve.

Those who did not have a warning stroke were more likely to have a more serious stroke than those who did have the warning stroke. Those with no warning were more likely to die while at the hospital (15.2 percent compared to 12.7 percent), more likely to have a heart arrest while in the hospital (4.8 percent compared to 3.1 percent) and less likely to be able to go home after the hospital stay, rather than to a nursing home or rehabilitation center (40.1 percent compared to 43.1 percent).

Those with the warning stroke were typically older than those without warning strokes. They were also more likely to have diabetes, high blood pressure and heart problems.

"It's possible that the blood vessels of those with warning strokes were preconditioned to the lack of blood flow, which protected them from the full result of the larger stroke. Any person who experiences even a minor stroke should get to the emergency room immediately."

The study was supported by the Canadian Institutes of Health Research and Ontario Ministry of Health and Long-Term Care.