WASHINGTON — More than 1 in 4 adults who bought insurance for themselves or their families last year had to skip needed medical care because they couldn’t afford it, according to study released Thursday by Families USA, a consumer health group.

Some signed up for coverage on the new health insurance exchanges under the Affordable Care Act and received financial assistance to help pay their premiums and some of their out-of-pocket costs. Others bought their plans directly from insurance companies.

Even with the gains under the health care law, 25.2 percent of adults who bought insurance on their own last year said they went without medical tests or treatments, prescription drugs or doctor visits because of cost. Because most adults who buy insurance on their own do not have dental care as part of their health coverage, the ability to see a dentist was not included in the main part of the report.

But when dental care is added to the mix, it becomes the most common type of care that adults skip because of its cost.

Hardest hit were lower- to middle-income adults. That’s someone who earned from $16,200 to $29,199 last year, or a family of three earning from $27,400 to $49,499. Almost 1 out of 3 of these adults said they went without needed medical care because the out-of-pocket cost was too high.

The main reason was health plans with a high deductibles, the amounts consumers owe for covered health care services before their insurance plans begin to pay. The report defines high deductibles as $1,500 or more per person.

More than half of adults had deductibles of $1,500 or more, and 30 percent had “exceedingly high deductibles” of $3,000 or more.

Health insurance has been getting less and less generous in recent years for many Americans, experts say, making it difficult for them to pay for care even when they have insurance, a trend that predates the Affordable Care Act.

The health law has led to more people getting insurance, and it provides for financial help in the exchanges for those with low incomes. But for many of those newly insured under the law, affording care is still a challenge because deductibles and co-pays are often high, experts say.

The numbers in the report come from data collected by the Urban Institute, which surveys a nationally representative sample of about 7,500 non-elderly adults every quarter. The sample in this analysis includes 1,229 such adults with incomes above 138 percent of the federal poverty level.