The gains in the numbers of those who could afford to pay their bills were seen in Medicaid expansion states and states that decided not to expand Medicaid, as permitted in the reform act.

In the expansion states, the percent who couldn’t afford coverage fell from 20.5 percent to 15.4 percent. In non-expansion states, the dip was still significant, as the percentage fell from 24.6 percent to 20.4 percent.

The usual reasons — low income and high deductible coverage — continued to characterize those who had trouble paying medical bills: 24.4 percent of those with incomes at or below 138 percent of the federal poverty level had trouble paying, compared to 14.4 percent of those with incomes above the threshold.

Those who had trouble with their bills tended to go without dental care or didn’t buy prescription drugs, both basic medical care components.

The researchers said expanded access to affordable health care should continue to reduce the number of those who cannot afford complete medical care. But it won’t completely eliminate the pressure families will feel when the insurance or hospital bills arrive.

“It’s encouraging to see that fewer families report problems with medical bills, but at the same time it’s very clear that health insurance does not provide immunity from financial distress,” said Kathy Hempstead, who leads coverage issues at the Robert Wood Johnson Foundation. “Affordability remains our biggest health care challenge – affecting both enrollment in coverage as well as access to care for those who are covered.”