Supporters of President Obama's health care law had predicted that expanding insurance coverage for the poor would reduce costly emergency room visits because people would go to primary care doctors instead. But a rigorous new experiment in Oregon has raised questions about that assumption, finding that newly insured people actually went to the emergency room a good deal more often.
The study, published in the journal Science, compared thousands of low-income people in the Portland area who were randomly selected in a 2008 lottery to get Medicaid coverage with people who entered the lottery but remained uninsured. Those who gained coverage made 40 percent more visits to the emergency room than their uninsured counterparts during their first 18 months with insurance.
The pattern was so strong that it held true across most demographic groups, times of day and types of visits, including those for conditions that were treatable in primary care settings.
The findings cast doubt on the hope that expanded insurance coverage will help rein in emergency room costs just as more than two million people are gaining coverage under the Affordable Care Act. And they go against one of the central arguments of the law's supporters, that extending insurance to large numbers of Americans would reduce emergency room use, and eventually save money.
In remarks in New Mexico in 2009, Mr. Obama said: "I think that it's very important that we provide coverage for all people because if everybody's got coverage, then they're not going to the emergency room for treatment."
The study suggests that the surge in the numbers of insured people may put even greater pressure on emergency rooms, at least in the short term. Nearly 25 million uninsured Americans could gain coverage under the law, about half of them through Medicaid. The first policies took effect on Wednesday.
"I suspect that the finding will be surprising to many in the policy debate," said Katherine Baicker, an economist at Harvard University's School of Public Health and one of the authors of the study.
An administration spokeswoman, Tara McGuinness, said that the time frame was too short to expect much of a change, and that over the longer term, use would most likely decline. She pointed to a longer-term study in Massachusetts, which expanded coverage for its residents in 2006, that found an 8 percent decline in emergency department use over a period of several years.
"Medicaid saves lives and improves health outcomes," Ms. McGuinness said. "Plenty of studies show that."
But many economists say that the emphasis on emergency room use, both in policy and in political speeches, is misplaced, as it makes up only a small part of health care costs in the United States. A federal government health survey found that emergency departments accounted for about 4 percent of total health spending in 2010, far less than inpatient hospital visits, which accounted for about 31 percent. Certain populations, however, like low-income people with chronic illnesses, have much higher rates of use.
Dr. Baicker and Amy Finkelstein, an economist at the Massachusetts Institute of Technology, another author, said the increased use of emergency rooms is driven by a basic economic principle: When services get less expensive, people use them more. Previous studies have found that uninsured people face substantial out-of-pocket costs that can put them in debt when they go to the emergency room. Medicaid reduces those costs.
Medicaid coverage also reduces the costs of going to a primary care doctor, and a previous analysis of data from the Oregon experiment found that such visits also increased substantially.
"This is just one piece of an increase we found across every type of care," said Bill J. Wright, an author of the new study who is the associate director of the Center for Outcomes Research and Education in Portland, a part of Providence Health and Services, a large health care provider.
The study's authors emphasized that Medicaid had many benefits. Previous analyses from the experiment found that gaining coverage reduced the incidence of depression and increased feelings of financial stability.
The study drew on data from the Oregon Health Insurance Experiment that included about 90,000 low-income Oregonians and randomly assigned about 30,000 of them access to Medicaid. Health experts say the experiment's design — random assignment of coverage through a lottery — allowed them to isolate and evaluate the effects of the program. Such designs are the gold standard in medical research, but are rarely used for domestic health care policy.
Some experts noted that the study measured only the first 18 months after people gained coverage, and that old habits of relying on the emergency room are often hard to shake. It also takes time to find a primary care doctor and make an appointment.
"How to use a plan and when to seek emergency department care involves a learning curve that doesn't happen overnight," said Sara Rosenbaum, a health researcher at George Washington University who was not involved in the study.
Amitabh Chandra, a professor and director of health policy research at the Harvard Kennedy School of Government, said people may often use the emergency room because they need its services. Medicine has become increasingly complex, with teams of specialists using highly sophisticated equipment for treatments that often go beyond the capabilities of the family doctor.
"We often say, 'If this person had just received preventative care at a doctor's office, we would not have seen emergency room use,' " said Dr. Chandra, who was not involved in the study. "But there is only so much that prevention can do."
Professor Rosenbaum pointed out that a lot of the recent growth in emergency department use has been among the privately insured people, not the uninsured. She said insurers often recommend going to the emergency room for quick specialty care, like for stomach pain.
Dr. Wright said that many participants in Oregon were already connected to a primary care doctor, and that it was unlikely that the rise in use had much to do with a lack of access to a physician. The study's lesson, he said, was that new coverage needed to be accompanied by broader changes to the way care was delivered, like those in Oregon and under Mr. Obama's new law.
Heidi Allen, an assistant professor at Columbia University and an author of the study, said much of the non-urgent emergency department use among patients she interviewed happened because those patients could not get same-day appointments with their primary care doctors.
Dr. Chandra, who helped conduct another analysis of emergency department use in Massachusetts after the overhaul, called the Oregon study, with its strong design and clear result, "breathtaking." In contrast, studies from Massachusetts have come up with conflicting findings. His study, for example, found that emergency room use did not change.
"You would conclude what you wanted to conclude depending on which side of political aisle you were on," he said, adding, "Now we have an answer."
