Nearly a quarter of U.S. adults who were insured all last year lacked adequate protection from big medical bills based on their income, according to Commonwealth Fund research.
The nonprofit foundation estimates that about 31 million people between the ages of 19 and 64 were underinsured due in part to the out-of-pocket expenses they have to pay for care. That includes deductibles, or payments a patient has to make before most coverage begins.
Insurers and employers who offer coverage have been raising deductibles for years as they try to contain premiums, or the price of insurance coverage. That means more of the bill for care is being passed along to patients. Some benefits advisers say this approach can help lower health care costs because it compels patients to shop for better deals on care, and insurers and employers are providing tools for patients to do that.
Skipping care altogether is another approach patients are choosing, according to Commonwealth. It found that 44 percent of the people considered underinsured skipped doctor's visits or a prescription or did not get a recommended medical test.
Commonwealth found that 51 percent of the underinsured had problems paying medical bills or were paying off debt over time.
Almost 60 percent of underinsured adults had coverage through an employer, the most common form of health insurance in the United States. Rates were highest among those working for small firms.
Commonwealth considers most people to be underinsured if their out-of-pocket costs — a total that doesn't include the premium — equal 10 percent or more of their household income. The foundation uses a lower percentage for those with incomes close to federal poverty levels.
It compiled its estimates using data from a health insurance survey conducted in the second half of last year. The telephone survey involved a random sample of more than 6,000 adults.
Overall, the percentage of adults considered underinsured has stayed fairly stable since 2010 but has nearly doubled since 2003.
The federal health care overhaul expanded insurance to millions of U.S. residents last year, with many gaining coverage with help from income-based tax credits or subsidies. Commonwealth said it could not assess the overhaul's impact on underinsurance.
The New York-based Commonwealth Fund is a private foundation dedicated to expanding coverage and improving health care quality. While those goals generally align with the overhaul, the foundation is non-partisan.