New York ? People with insurance are increasingly using emergency rooms, even for nonurgent care, a study found — perplexing experts who thought the uninsured were the chief reason for ER overcrowding.

Emergency room visits jumped to an average of 107.7 million a year in 2001 and 2000, up 16.3 percent from 1996 and 1997. Most of the increase came from insured patients, according to the Center for Studying Health System Change, a Washington think tank.

Privately insured patients’ use of the emergency room rose 24.3 percent to 43.3 million visits over that six-year period. People covered by Medicare, the government insurance for the elderly, visited the ER 16 million times, a 10 percent increase. Visits by uninsured patients rose 10.3 percent to 18 million, while those by patients covered by Medicaid, the government program for the poor, were flat at 18.4 million.

Only 46 percent of the ER visits by privately insured patients were considered either emergent — requiring care within 15 minutes of arrival — or urgent — requiring care within an hour of arrival.

“The results were surprising,” said Peter Cunningham, a senior health researcher at the Center for Studying Health System Change, who conducted the study using data from the Centers for Disease Control and Prevention as well his organization’s own information.

“Uninsured people clearly are not a major factor in increased crowding at most hospital emergency departments, but uninsured people’s growing reliance on emergency care indicates decreased access to other sources of care.”

The American Hospital Assn. says 67 percent of emergency rooms are at or over capacity. At inner-city hospitals, that number jumps to 80 percent.

Some experts speculate that more patients are turning to the ER because doctor’s offices do not accommodate people’s working schedules. Emergency rooms are open 24 hours a day, and no appointments are necessary.

And some people may go to the emergency room believing they have a true medical emergency, even though it turns out be a minor problem.

“Sometimes people think they are having a heart attack and it is only bad indigestion,” said Carmela Coyle, senior vice president for policy at the American Hospital Assn.