While federal and state policymakers have argued that expanding Medicaid would reduce costly and inefficient use of hospital emergency rooms by increasing access to primary healthcare, the Science study suggests this is not the case.
"When you cover the uninsured, emergency room use goes up by a large magnitude," said senior study author and MIT economics professor Amy Finkelstein. "In no case were we able to find any subpopulations, or type of conditions, for which Medicaid caused a significant decrease in emergency department use."
The study sample, made up mostly of white urban-dwelling patients, showed an increase in ER use after 18 months, and the increase was larger for men than it was for women.
The study was tied to a 2008 Medicaid expansion program in Oregon, in which officials held a lottery to enroll 30,000 eligible adults out of a total pool of 90,000.
Among other eligibility requirements, participants had to be between the ages of 19 and 64 and earn less than $10,400 a year as an individual, or less than $21,200 for a family of four.
When surveyed by researchers, Medicaid recipients said coverage had helped improve their general health, reduce depression and relieve financial pressure, although medical data failed to show a significant change in measurable health indicators such as blood pressure and cholesterol levels, the study authors wrote.
Researchers also noted that while new Medicaid recipients said that coverage had increased their access to primary care physicians, prescription drugs and preventive care, a review of data for 12 Portland hospitals showed a surge in ER use.
The increased use, authors wrote, was solely the result of outpatient visits; it was not accompanied by an increase in actual hospital admissions.
In fact, the increased use was most pronounced in cases classified as "primary care treatable" and "non-emergent," authors wrote. Statistically significant increases were found in several specific conditions: injuries, headaches and chronic conditions.
"These findings speak to one cost of expanding Medicaid, as well as its net effect on the efficiency of care delivered, and may thus be a useful input for informed decision-making balancing the costs and benefits of expanding Medicaid," the authors concluded.
The study is one of only a few to examine the issue of government healthcare expansion, and is unlikely to end debate on the matter. Previous studies that analyzed the 2006 health insurance expansion in Massachusetts found either unchanged or reduced use of emergency departments.
In an accompanying editorial, economist Raymond Fisman, of the Columbia Business School, said the study was clear evidence that providing health coverage to the poor would naturally increase use of hospital emergency rooms.
"These findings explode the myth that health insurance access will reduce the strain on emergency services and thus undermine the hope that expanded coverage will put an end to this particular inefficiency in America's bloated healthcare market," Fisman wrote.
However, it would be a mistake to believe that these low-income patients are seeking "unnecessary care," he said.
Previous studies have indicated that patients are in fact directed to the emergency room by primary care physicians.
"Primary care practices fill their schedules with appointments for regular, predictable treatment and are de facto using ERs as a referral for urgent or time-consuming cases," Fisman wrote.
While Fisman acknowledged that Portland may look very different than the rest of the United states, there was no reason to expect that expansion of health coverage in other states would not result in increased ER use.
"Whether or not you think universal coverage is a good idea, we had better start planning for it," Fisman wrote.
[For the record, 10:04 a.m. PST Jan. 6: An earlier version of this post misspelled the last name of economist Raymond Fisman of the Columbia Business School as Fishman.]