U.S. healthcare costs are among the world's highest, and 1 in 4 adults with health coverage struggle with high out-of-pocket costs, a new survey shows.

The survey — by the Commonwealth Fund, a healthcare focused think tank — finds that most people have coverage offered by employers, but their policies don't always provide timely or affordable access to care. 

As a result, many Americans don't get needed prescriptions filled and skip ongoing care, causing their health problems become worse and more costly to treat. 

"Millions of families across the U.S. can't afford the care they need, including many who are managing chronic conditions like diabetes and heart disease," said Dr. Joseph Betancourt, a primary care physician who is president of the Commonwealth Fund. 

"I routinely see patients facing unexpected costs that prevent them from getting essential care to stay well and avoid illness," he said in a Commonwealth Fund news release. "At the end of the day, these financial barriers ripple through our health care system, driving up costs — with preventable hospitalizations being just one of many costly consequences."

Between March and June, the Commonwealth Fund asked a representative sample of 18- to 64-year-old Americans about their health insurance experiences.

The survey showed that about 20% had been uninsured during the year, and 23% of those who had insurance were enrolled in plans with high out-of-pocket costs that make it hard to afford care.

In all, more than half of respondents (57%) said cost prompted them to forgo needed care, and 44% had medical debt.

As many as a third of people with chronic conditions, such as diabetes or heart failure, said they couldn't afford to fill needed prescriptions.

"The Affordable Care Act has covered 23 million people and cut the uninsured rate in half," said study lead author Sara Collins, senior scholar at the Commonwealth Fund. "But high costs are a serious problem for many Americans, regardless of the kind of insurance they have."

The survey revealed that 66% of underinsured Americans had employer-provided health insurance; 14% had individual plans or those from the healthcare marketplace; and 11% had Medicaid, a government program which insures low-income people and those with disabilities.

Even with insurance, costs can mount.

More than a third of working-age respondents who were uninsured or underinsured said they were paying off medical or dental debt. Nearly half of them owe $2,000 or more and 21% owe $5,000 or more.

Roughly half of adults with debt incurred it while getting hospital treatment for an ongoing health issue.

Two in 5 adults who skipped or delayed care because of cost said their health deteriorated as a result. Lower-income respondents were especially hard-hit.

"Ensuring that all Americans have access to affordable, comprehensive coverage is critical not only to people's health and economic security, but also for a strong health care system," Betancourt said.

The study noted that 10 states have not widened eligibility for Medicaid coverage under the Affordable Care Act, leaving 1.5 million people uninsured. Besides calling for establishment of a federal fallback option to cover those people, the report suggested several other steps to provide better coverage to more people.

They include permanently extending tax credits for buying coverage on the healthcare marketplace. Enacted during the pandemic, they are set to expire next year. Without the credits, annual premium costs on the marketplace will spike by $705, on average. An estimated 4 million people could lose coverage.

Other policy recommendations included:

Enforce tough requirements on hospitals to prevent patients from accumulating debt and remove medical debt from credit reports; lower deductibles and out-of-pocket costs in marketplace plans; make employer-provided coverage more affordable and comprehensive for low-wage workers; let states maintain 12 months of continuous Medicaid eligibility for adults as has been done for children, to prevent lapses in coverage.

"Congress, employers, insurers and health care providers all play a role in lowering costs and making care more affordable, so families can avoid debt and get the care they need to stay healthy," Collins said.

The survey, conducted by phone and online, included 8,201 adults age 19 or older.