People who get to a hospital no more than an hour after having the first symptoms of a stroke are twice as likely to get the powerful clot-dissolving drug that is the first line of treatment, a new study finds.Of the more than 100,000 people treated for stroke at American hospitals, 27.1 percent of those whose treatment began within a hour of the first symptoms received tissue plasminogen activator (tPA), according to a report to be delivered Wednesday at the American Stroke Association’s International Stroke Conference, in San Diego.

Only 12.9 percent of those arriving between one and three hours of symptom onset received the drug, the study found.

The study results “are both good news and bad news,” said study author Dr. Jeffrey L. Saver, director of the stroke center at the University of California, Los Angeles. “The good news is that the message is getting through to a partial extent. We’re getting early treatment to a lot more people than we ever expected. The bad news is that only about a quarter of patients are getting to hospitals within an hour of having stroke symptoms.”

The results apply only to those hospitals in the American Heart Association’s “Get With the Guidelines” program, Saver noted.

Today’s report did not discuss the outcome of quick treatment, Saver added. But preliminary analysis indicates that “for every 100 patients treated, 30 benefit and three are harmed,” he said.

Use of tPA is the only approved treatment for the 80 percent or more of strokes caused by blockage of a brain artery by a blood clot. (The others are the result of an artery rupture.) But the drug must be used within three hours after stroke symptom onset.

Get With the Guidelines-Stroke is the stroke association’s program aimed at increasing appropriate use of tPA therapy for ischemic strokes, those caused by blood clots.

Saver and his colleagues looked at the records of 106,924 people treated for ischemic strokes at 905 hospitals. They found that 28.3 percent of them arrived within 60 minutes of stroke onset, 31.7 percent arrived one to three hours after symptoms started, and 40.1 percent arrived more than three hours after symptoms started.

That last number indicates that “we have a great deal of additional work to do in educating the public and stroke center staffs,” Saver said in a statement. “For every minute in which blood flow is not restored, nearly 2 million additional blood cells die.”

Stroke symptoms include sudden numbness or weakness of the face, arm or leg, especially on one side of the body; sudden trouble speaking or understanding; sudden trouble seeing in one or both eyes; or sudden, severe headache.

When such symptoms occur, emergency help should be sought by calling 911 or a local emergency medical service number, the stroke association recommends.

In the study, those people who arrived at a hospital within an hour of symptom onset were more likely to suffer serious brain damage, indicating that the symptoms which led to them seeking help were more severe, the researchers said.

The Get With the Guidelines-Stroke program now covers more than 800,000 people treated at more than 1,400 hospitals, said study co-author Dr. Lee Schwamm, an associate professor of neurology at Harvard Medical School.

“This data registry can contribute significantly to our understanding of acute stroke care and outcomes,” he said in a statement.

About 800,000 Americans have strokes each year, and about 300,000 die of them.