Private health insurance gives patients a far better chance of getting appointments within a week of treatment than does Medicaid or no insurance at all, according to the study of 430 clinics in nine U.S. cities.

The findings shatter the myth that "when people really need care, they get it," said lead author Dr. Brent Asplin, head of emergency medicine at Regions Hospital in St. Paul, Minn. Delays in urgent outpatient treatment put patients at risk for life-threatening conditions, he said.

But even Americans with private health insurance - about 180 million - are at risk, according to the study, which found that private insurance wasn't a guarantee of timely access.

Co-author Dr. Karin Rhodes, an emergency physician at the University of Chicago, said she fairly frequently sees patients return to the emergency room in a deteriorated condition because they didn't receive timely follow-up care.

About 45.8 million Americans are uninsured and 53 million others are covered by Medicaid, the government-funded program for low-income people.

"As a nation, we've got to find a way to provide health insurance coverage for everybody, not just those who are employed" or able to pay for private insurance, Coyle said.

The study, appearing in Wednesday's Journal of the American Medical Association, comes amid growing pressure to avoid hospitalizing all but the sickest patients treated in emergency rooms - a strategy that depends on timely access to follow-up care, the researchers said.

Clinics involved in the study were in the cities of Atlanta; Chicago; Dallas-Fort Worth; Denver; Jacksonville, Fla.; Los Angeles; Minneapolis-St. Paul; New York; and Phoenix.