WASHINGTON (Reuters) - Mini-strokes lead to a major stroke within a week in one out of 20 people and should be treated as a medical emergency, British doctors said on Sunday.

They said people who were immediately treated for the small strokes, called transient ischemic attacks, or TIAs, had almost no risk of a major stroke soon afterward. But people who did nothing about a TIA had an 11 percent risk of a major stroke within a week, Dr. Matthew Giles and Peter Rothwell of the Stroke Prevention Research Unit at the University of Oxford reported.

For their study, published in the Lancet Neurology, Giles and Rothwell combined results from 18 different groups of patients, a total of more than 10,000 people. Overall, 5 percent of patients had a major stroke within seven days of a TIA, they found. Just under 1 percent of patients treated for a TIA at a specialist neurology clinic went on to have a major stroke within a week, compared with 11 percent of those who ignored the TIA, they found.

"The risk of stroke reported amongst patients treated urgently in specialist units was substantially lower than risks reported among other patients treated in alternative settings," they wrote. "These results support the argument that a TIA is a medical emergency and that urgent treatment in specialist units may reduce the risk of subsequent stroke."

Most strokes are caused by a blockage to one of the arteries in or leading to the brain. A small percentage of strokes are hemorrhagic, caused when a blood vessel blows out. TIAs are smaller versions of major strokes and cause similar symptoms -- dizziness, weakness of an arm or leg or visual disturbances. People who have larger strokes may be paralyzed on one side or lose their ability to speak. More than two-thirds of major stroke survivors have some type of disability. .