Policymakers frequently point to Medicaid patients high use of the emergency room for routine care as one factor driving up health-care costs.

There’s just one problem with that claim: A new study finds it’s not true.

The majority of Medicaid visits to the emergency room are for urgent or serious issues, according to research published Wednesday by the Center for Studying Health System Change.

Both those covered by Medicaid and those on private insurance use the emergency department at the same rate for both emergency and non-urgent care.

“There’s this perception that Medicaid patients go to the emergency department for very little things that could easily be addressed elsewhere,” said study author Emily Carrier. “What we found here is that Medicaid patients use the emergency department for the same reason as the privately insured.”

Medicaid patients do have a significantly higher rate of emergency department use. In 2008, Medicaid enrollees had 45.8 emergency room visits per 100 enrollees, compared to 24 visits for the same number of privately insured individuals.

When Medicaid patients went to the emergency room, it turned out, they did so for largely acute medical problems. Three-quarters of the Medicaid visits were categorized as emergent, urgent, or semi-urgent. Among those with private coverage, the number stood at 78 percent.

“People may see a higher rate of emergency department use among Medicaid patients and think they go at higher levels for routine care,” Carrier said. “I don’t think there’s been a lot out there, before this, exploring whether that’s actually the case.”

States with recession-squeezed budgets have taken some actions to tamp down on Medicaid patients’ use of the emergency room for routine care. Washington state announced in April it would no longer pay for “unnecessary” Medicaid visits to the emergency department. Iowa and Tennessee have also taken similar actions.

If those unnecessary visits are few and far between, as this study suggests, those policies would be unlikely to change how Medicaid patients receive care.

“This research turns the conventional wisdom on its head,” said Karoline Mortensen, a University of Maryland professor whose research focuses on patterns of care among low- income Americans. “It’s critical for policy solutions that we have a better understanding of the problem. The blunt instrument of saying we won’t pay for those visits isn’t going to be effective in a situation like this.”

Mortensen’s own research has looked at how implementing a co-payment in Medicaid changes emergency department use. She published a 2010 study finding that such policies had no impact on patterns of care — and thinks this new paper helps explain why.

“There’s a misconception that people decide they can’t get to their primary care doctor, so they will hang out in the emergency room all day,” said Mortensen. “This is saying, that’s not really the case.”

This new study adds to a growing body of research aiming to understand how Medicaid patients use health care, developing at the same time that governors weigh whether to participate in the health law’s Medicaid expansion.

Researchers have used Oregon’s 2008 Medicaid expansion — where some low-income residents gained coverage via a lottery, from a pool of 89,000 applicants — to understand how the program affects peoples’ lives.

The study found that those who gained Medicaid coverage reported being in better mental and physical health, and were less likely to have unpaid medical bills.

What did not change, however, were patterns of emergency department use. Both those who gained Medicaid — and those without insurance — used the emergency department at the same level.

“We have no evidence that Medicaid reduces emergency department use,” said Harvard University’s Katherine Baicker, a co-author of the study.

Baicker and her colleagues have, so far, only analyzed self-reported data on emergency department use. In forthcoming research, they will look at hospitals’ administrative data to understand what type of medical conditions individuals sought treatment for in the emergency room.

One question this new study did not answer was why Medicaid patients have a higher rate of emergency department use to begin with. It could have something to do with the fact that Medicaid tends to cover higher-risk patients, like the disabled and pregnant women.

It may also reflect a lack of access to primary care, as some surveys show a shrinking number of doctors who accept new Medicaid patients. If health problems go untreated, the thinking goes, they could become worse and ultimately result in an emergency room visit.

“The misconception is that Medicaid patients get their primary care at the emergency department,” said Maryland’s Mortensen. “We see in this study that’s not true, but we don’t know if they’re getting their primary care elsewhere.”