Many people newly insured by Medicaid under the federal healthcare law are seeking treatment in hospital emergency rooms, one of the most expensive medical settings, a study released Monday concludes.

The study also found indications that newly insured Medicaid patients admitted to hospitals may be sicker than patients previously covered under the same program, which serves more than 60 million low-income and disabled people.

Researchers looked at data reported by 450 hospitals in 25 states, through the middle of this year. Thirteen of the states expanded Medicaid, and 12 states did not.

Looking at the broad sample of 25 states, the study found that the average number of ER visits in states that expanded Medicaid increased by 5.6 percent, when the second three months of this year were compared with the same period in 2013. That increase was more than three times bigger than experienced by hospitals in states that did not expand. It was also outside the range of normal year-to-year fluctuations, Tholen said.