New research suggests that adults who have their medical care covered by Medicaid use emergency rooms 40% more than adults in similar situations who do not have health insurance. This is according to a study published in the journal Science.

Medicaid is a governmental program that provides medical and health-related services to individuals and families in the US who have low incomes and limited resources.

Eligibility for Medicaid varies in each state, but the majority of states offer the program for adults with children below a certain income threshold, pregnant women, many elderly people and those with disabilities.

In 2008, the state of Oregon introduced a Medicaid lottery to assign the health insurance to an additional 10,000 low-income adults after realizing they had additional funds for the program.

Individuals in Oregon are eligible to apply for the lottery if their annual income is below the federal poverty level set by the US Department of Health and Human Sciences. For 2013, this is approximately $23,550 for a family of four and $11,490 for a single person.

The study researchers, from the Massachusetts Institute of Technology (MIT) and the Harvard School of Public Health, say the lottery system implemented in Oregon led to a group of state residents gaining Medicaid coverage who had similar circumstances to individuals who still did not have coverage, meaning a comparison could be made between the two groups.

With this in mind, the investigators took the opportunity to carry out a randomized controlled evaluation of Medicaid by analyzing emergency room records for around 25,000 individuals over 18 months.

From this, not only did the researchers find that people with Medicaid used emergency rooms 40% more than those without health insurance, but also they found that Medicaid routinely increases the number of emergency room visits.

This was consistent across all demographic groups, all types of visits and all medical conditions – even those that could be treated in primary care settings, according to the researchers.

Commenting on the findings, Amy Finkelstein of MIT and a principal investigator of the study, says:

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.

Although one always needs to be careful generalizing to other settings, these results suggest that other Medicaid expansions are unlikely to decrease emergency room use.”

The investigators note that their findings are applicable to the whole of the US, since the introduction of the Affordable Care Act is likely to cause many states to see expansion of Medicaid at levels similar to that seen in Oregon following the lottery.

They add that their findings also present new evidence for ongoing debates about how the expansion of Medicaid will impact medical costs and the care provided by emergency rooms.

The researchers point out that their findings support traditional beliefs that health insurance increases the use of medical care by “lowering out-of-pocket costs.”

They say previous research has suggested that Medicaid may reduce emergency department visits, as reducing the “out-of-pocket” costs may push more people into the use of primary and preventive care. But Finkelstein says the results in this study showed that Medicaid expansion primarily increases the use of emergency services.

However, she notes that further research is needed to clarify the results of the study, as “they could have gone either way.”

Earlier this year, Medical News Today reported on a study suggesting that uninsured low-income adults have better overall health, compared with those who are covered by Medicaid.